PAP-10430: split Issue-to-Task copy migration (#7651)

## Thinking Path

> - Paperclip is the open source app people use to manage AI agents for
work.
> - The board UI is the operator surface where users create, assign,
monitor, and review work items.
> - The product language is moving toward "tasks" for user-facing work
items while the internal API and database still use "issues".
> - PR #7543 bundled this copy migration with broader
information-architecture work, which made the branch too large for
Greptile review.
> - This pull request peels the Issue-to-Task copy migration into a
smaller, independently reviewable change.
> - The benefit is clearer user-facing terminology, less agent confusion
via the Paperclip skill note, and a smaller PR that Greptile can review.

## Linked Issues or Issue Description

Refs #7645
Refs #7543
Refs PAP-10430

This PR was split out of #7543 so the Issue-to-Task copy migration can
be reviewed separately and the remaining IA PR can fall under Greptile's
file limit.

## What Changed

- Preserves Scott Tong's original `PAP-57` copy-only commit, with author
and co-author credit intact, to rename user-facing "Issues" copy to
"Tasks" across the UI while keeping routes/API/internal symbols as
`issue`.
- Updates onboarding and release-smoke browser selectors from `Create &
Open Issue` to `Create & Open Task`.
- Adds a terminology note to `skills/paperclip/SKILL.md` clarifying that
task and issue refer to the same Paperclip work item.
- Resolves the only cherry-pick conflict by keeping current search
artifacts support and changing visible search copy to "tasks".

## Verification

- `pnpm --filter @paperclipai/ui build` passed.
- `NODE_ENV=test pnpm exec vitest run
ui/src/components/IssuesList.test.tsx ui/src/components/Sidebar.test.tsx
ui/src/components/NewIssueDialog.test.tsx
ui/src/pages/IssueDetail.test.tsx` passed: 4 files, 66 tests.
- `git diff --check origin/master...HEAD` passed.
- Diff is 80 files, below Greptile's 100-file limit.
- Before/after UI copy examples: "Issues" -> "Tasks", "New Issue" ->
"New Task", "Create & Open Issue" -> "Create & Open Task".

## Risks

- Medium copy-risk: this intentionally changes user-facing terminology
broadly while keeping internal issue identifiers and routes unchanged.
- Some docs and APIs still say `issue`; the skill note clarifies this so
agents do not treat task and issue as separate entities.
- Browser-level visual validation is expected from CI because this local
container is missing usable browser dependencies.

> For core feature work, check [`ROADMAP.md`](ROADMAP.md) first and
discuss it in `#dev` before opening the PR. Feature PRs that overlap
with planned core work may need to be redirected — check the roadmap
first. See `CONTRIBUTING.md`.

## Model Used

Scott Tong authored the original `PAP-57` copy migration, assisted by
Claude Opus 4.8 and Paperclip agents per the preserved commit metadata.
Codex / GPT-5-class coding agent with shell, GitHub CLI, and repository
access performed the PR split, conflict resolution, skill note, and
verification.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have searched GitHub for duplicate or related PRs and linked
them above
- [x] I have either (a) linked existing issues with `Fixes: #` / `Closes
#` / `Refs #` OR (b) described the issue in-PR following the relevant
issue template
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] If this change affects the UI, I have included before/after
screenshots
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] All Paperclip CI gates are green
- [x] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge

---------

Co-authored-by: scotttong <scott.tong@gmail.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
Co-authored-by: Paperclip <noreply@paperclip.ing>

ui/src/components/IssuesList.test.tsx

@@ -452,12 +452,12 @@ describe("IssuesList", () => {
     );
 
     await waitForAssertion(() => {
-      const button = container.querySelector<HTMLButtonElement>('button[aria-label="New issue in Feature Branch"]');
+      const button = container.querySelector<HTMLButtonElement>('button[aria-label="New task in Feature Branch"]');
       expect(button).not.toBeNull();
     });
 
     await act(async () => {
-      const button = container.querySelector<HTMLButtonElement>('button[aria-label="New issue in Feature Branch"]');
+      const button = container.querySelector<HTMLButtonElement>('button[aria-label="New task in Feature Branch"]');
       button?.dispatchEvent(new MouseEvent("click", { bubbles: true }));
       await Promise.resolve();
     });
@@ -884,7 +884,7 @@ describe("IssuesList", () => {
       container,
     );
 
-    const input = container.querySelector('input[aria-label="Search issues"]') as HTMLInputElement | null;
+    const input = container.querySelector('input[aria-label="Search tasks"]') as HTMLInputElement | null;
     expect(input).not.toBeNull();
     const valueSetter = Object.getOwnPropertyDescriptor(window.HTMLInputElement.prototype, "value")?.set;
     expect(valueSetter).toBeTypeOf("function");
@@ -1157,7 +1157,7 @@ describe("IssuesList", () => {
     );
 
     await waitForAssertion(() => {
-      expect(container.textContent).toContain("Some board columns are showing up to 200 issues. Refine filters or search to reveal the rest.");
+      expect(container.textContent).toContain("Some board columns are showing up to 200 tasks. Refine filters or search to reveal the rest.");
     });
 
     act(() => {
@@ -1187,7 +1187,7 @@ describe("IssuesList", () => {
 
     await waitForAssertion(() => {
       expect(container.querySelectorAll('[data-testid="issue-row"]')).toHaveLength(100);
-      expect(container.textContent).toContain("Rendering 100 of 220 issues");
+      expect(container.textContent).toContain("Rendering 100 of 220 tasks");
     });
 
     act(() => {
@@ -1226,7 +1226,7 @@ describe("IssuesList", () => {
 
     await waitForAssertion(() => {
       expect(container.querySelectorAll('[data-testid="issue-row"]')).toHaveLength(250);
-      expect(container.textContent).toContain("Rendering 250 of 420 issues");
+      expect(container.textContent).toContain("Rendering 250 of 420 tasks");
     });
 
     act(() => {
@@ -1669,13 +1669,13 @@ describe("IssuesList", () => {
     );
 
     await waitForAssertion(() => {
-      const input = container.querySelector('input[aria-label="Search issues"]') as HTMLInputElement | null;
+      const input = container.querySelector('input[aria-label="Search tasks"]') as HTMLInputElement | null;
       expect(input).not.toBeNull();
       input?.focus();
       expect(document.activeElement).toBe(input);
     });
 
-    const input = container.querySelector('input[aria-label="Search issues"]') as HTMLInputElement;
+    const input = container.querySelector('input[aria-label="Search tasks"]') as HTMLInputElement;
     act(() => {
       input.dispatchEvent(new KeyboardEvent("keydown", {
         key: "Enter",
@@ -1705,13 +1705,13 @@ describe("IssuesList", () => {
     );
 
     await waitForAssertion(() => {
-      const input = container.querySelector('input[aria-label="Search issues"]') as HTMLInputElement | null;
+      const input = container.querySelector('input[aria-label="Search tasks"]') as HTMLInputElement | null;
       expect(input).not.toBeNull();
       input?.focus();
       expect(document.activeElement).toBe(input);
     });
 
-    const input = container.querySelector('input[aria-label="Search issues"]') as HTMLInputElement;
+    const input = container.querySelector('input[aria-label="Search tasks"]') as HTMLInputElement;
     act(() => {
       input.dispatchEvent(new KeyboardEvent("keydown", {
         key: "Escape",