feat(github): add /github page for PRs and issues (#687)

* feat(github): add /github page for PRs and issues

Dedicated page under /github lists pull requests and issues across the
authenticated user's repos with preset filters, custom GitHub search
queries, per-repo narrowing, saved queries, and one-click task launching
for any PR or issue.

Performance:
- Cache user PR/issue search responses for 30s with singleflight to
  coalesce concurrent misses, so preset switching and pagination avoid
  upstream round trips.
- Replace the per-row PR status fetch (N+1) with a batch endpoint
  POST /api/v1/github/prs/statuses that fans out concurrently on the
  backend with a semaphore and caches per-PR.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* style: apply Prettier formatting

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix: address review feedback on PR cache + status batching

- Harden searchCacheKey against separator collisions from
  user-controllable customQuery (length-prefix encoding).
- Drop repositories.loaded hydration when inner workspace fetch fails
  so the client refetches instead of trusting a partial snapshot.
- Guard useGitHubSearch with a monotonic request counter to drop
  stale responses when filter+page changes overlap.
- Fix usePRStatuses teardown: depend only on composed key so a new
  array identity per render doesn't cancel the in-flight batch.
- Correct godocs (duplicate, outdated state:open claim).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix: address additional review feedback

- Restore state:open for issue watcher: buildIssueSearchQuery no
  longer injects it as a default, so existing watches were starting
  to surface closed issues. Inject state:open in buildIssueFilter so
  only the watcher path is affected; the /github page presets already
  set their own state qualifiers.
- countCheckResults now excludes in-progress checks from the denominator
  so a `1/3` badge reflects pass rate on completed checks, not a mix of
  running and failed. The pending state is still carried via ChecksState.
- usePRStatuses retries after a transient fetch error (only mark the
  key as completed once the fetch resolves). This also fixes missing
  badges under React Strict Mode's intentional double-mount, since the
  first effect's cleanup fires before the response lands and the guard
  stays unset for the second mount to retry.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* test(github): add tests for my-github hooks

Covers use-committed-query, buildParams from use-github-search,
use-saved-presets readStorage validation, use-known-repos recordForKey
accumulator semantics, and use-pr-statuses batch fetch lifecycle.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix: address review feedback on search cache and repo accumulator

- Clamp perPage before composing the search cache key so identical
  pages (e.g. perPage=150 and =100) share a cache entry instead of
  creating duplicates keyed on the raw value.
- Add resetKnownReposStore and call it on /github unmount so the
  module-level repo accumulator doesn't carry across navigations.
- Rename use-pr-statuses test to match its assertion (it verifies
  stale statuses are cleared when the key changes and fetch fails).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* style: apply Prettier formatting

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(web): distinguish blocked from dirty in PR mergeable badge

GitHub's blocked state (required reviews/checks/branch protection)
is not a merge conflict, so don't label it "Conflicts". Surface it
as "Blocked" with the pending tone; keep "Conflicts" for dirty.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* fix: address remaining /github code review comments

- Route PR status + batch through handleSearchError so ErrNoClient
  surfaces as 503 instead of 500 (matches the search endpoints).
- Sort workflow steps by position in the quick-task-launcher default
  pick, matching the convention in issue-watch-dialog.
- Make PresetItem keyboard-accessible: role=button, tabIndex, and
  Enter/Space handling on the wrapping div (it contains a nested
  delete button, so it can't itself be a button).
- Extract useRepoOptions out of useGitHubPageState to bring the hook
  back under the 100-line complexity limit.
- Honor ctx.Done() when acquiring the PR-status batch semaphore so a
  cancelled HTTP request releases queued goroutines instead of
  running each upstream fetch to completion.
- Clarify parsePaginationQuery doc: the upper bound (100) is enforced
  by clampSearchPage in the client layer, not here.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* fix(web): address /github review follow-ups

- Merge duplicate @/lib/utils imports in pr-list.
- Use rel="noopener noreferrer" on external PR/issue links (codebase
  convention) and add cursor-pointer per the UI guidelines.
- Rewrite onOpenSaveDialog as an explicit if-block so the callback
  returns void rather than boolean | void.
- Use PaginationEllipsis in its own PaginationItem so the ellipsis
  and the adjacent page link are separate list items instead of
  visually fused into a single cell.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* refactor(web): derive QuickTaskLauncher dialog state from props

Replaces the useEffect+setState anti-pattern with useMemo-derived state
driven directly by the payload prop. Drops the eslint suppression that
was needed for react-hooks/set-state-in-effect.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

---------

Co-authored-by: Kandev Agent <agent@kandev.dev>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/backend/internal/github/controller_test.go

@@ -35,6 +35,12 @@ func (s *stubClient) FindPRByBranch(context.Context, string, string, string) (*P
 func (s *stubClient) ListAuthoredPRs(context.Context, string, string) ([]*PR, error) {
 	return nil, nil
 }
+func (s *stubClient) SearchPRs(context.Context, string, string) ([]*PR, error) {
+	return nil, nil
+}
+func (s *stubClient) SearchPRsPaged(context.Context, string, string, int, int) (*PRSearchPage, error) {
+	return &PRSearchPage{PRs: []*PR{}}, nil
+}
 func (s *stubClient) ListReviewRequestedPRs(context.Context, string, string, string) ([]*PR, error) {
 	return nil, nil
 }
@@ -69,6 +75,9 @@ func (s *stubClient) ListRepoBranches(context.Context, string, string) ([]RepoBr
 func (s *stubClient) ListIssues(context.Context, string, string) ([]*Issue, error) {
 	return nil, nil
 }
+func (s *stubClient) ListIssuesPaged(context.Context, string, string, int, int) (*IssueSearchPage, error) {
+	return &IssueSearchPage{Issues: []*Issue{}}, nil
+}
 func (s *stubClient) GetIssueState(context.Context, string, string, int) (string, error) {
 	return defaultPRState, nil
 }