The /api/v1/repos/:owner/:name/issues routes move out of src/http/api.ts into src/http/api/issues.ts, unchanged #7450

Intent: same as #7444. Issue routes are among the most edited in the 5,751-line src/http/api.ts, so in a module of their own they stop colliding with every other route change.

Done:

• [ ] Every router.add(…, "/api/v1/repos/:owner/:name/issues…") moves to src/http/api/issues.ts as issueRoutes(router, …), in the shape of src/http/api/labels.ts. api.ts calls it once where the routes were. Helpers used only by them move with them.
• [ ] No route, status, body or header changes: the existing API and OpenAPI tests pass untouched and bun x tsc --noEmit is clean. The pull says how many lines api.ts lost.

Files: src/http/api.ts, src/http/api/issues.ts (new).

Risk: a pure move. Rebase over any sibling split that lands first; they touch different blocks.