feat: unify issue search semantics

[Codename-11]

Summary

• add one shared issue-search parser and Prisma predicate for tRPC list/count, MCP issues.list, and command-palette issue results
• recognize case-insensitive KEY-N, bare N, and #N as exact identifiers while preserving workspace, lifecycle, archive, facet, and API-key narrowing
• search operator-facing issue metadata for ordinary text and keep stable cursor page boundaries
• update Issues-page guidance, MCP/tRPC/product docs, DEVLOG, integration coverage, and Playwright acceptance coverage
• rebase the implementation onto the required v0.27.1 / 684df53 base

Verification

• pnpm lint (passes; pre-existing warnings only)
• pnpm typecheck
• 119 local container-backed Prisma migrations applied / no pending migrations
• pnpm test --no-file-parallelism with CI-equivalent local Postgres, Redis, and MinIO settings (183 files passed, 1 skipped; 1,425 tests passed, 1 skipped)
• fresh production E2E build
• pnpm exec playwright test tests/e2e/issues-scope.spec.ts --workers=1 (2 passed against dedicated local forge_e2e DB / Redis DB 15)
• git diff --check origin/main...HEAD

Safety

• no schema migration or search extension/index
• no notification, audit, dispatch, or LLM-wake behavior changed
• no merge, release, tag, or deployment performed

Implements AXI-119.

[Codename-11]

Self-review complete: no actionable findings. Reviewed shared identifier parsing/predicate composition, API-key narrowing, workspace/lifecycle/archive/facet composition, deterministic pagination, MCP/command-palette parity, and the focused regression coverage. GitHub CI is green across lint/typecheck/unit and both Playwright shards.

[Codename-11]

Updated-head review complete at 536fb69 after rebasing onto v0.27.1 / 684df53: no actionable findings. Re-reviewed shared identifier parsing, tenant and API-key scope composition, metadata predicates, deterministic ordering/cursor boundaries, MCP and command-palette parity, and regression coverage. Local lint, typecheck, 1,425-test Vitest gate, fresh production build, and focused Playwright journeys pass.