chore: remove dead SubscriptionRef layer and unused helpers

[fathiraz]

Summary

• Removes an Effect SubscriptionRef/Stream mirror bolted onto four pub/sub stores (queue, checkbox-portal, toast, selection) that had zero production consumers — the app uses each store's plain callback subscribe() API. getSelectionSnapshot is kept (used by selection-control.tsx).
• Deletes src/lib/store-streams.test.ts, which only tested the removed selectionChanges/toastChanges streams.
• Removes dead helper clusters in bulk-edit-utils.tsx, bulk-duplicate-utils.tsx, and bulk-actions-utils.tsx, plus a handful of standalone unused exports (SEARCH_OWNER_REPOS, sprintProgress, SecondaryAction, CircleCheckIcon, UnpinIcon, disposeRuntime, resetHovercardAppendTargetForTests, DistributionFunction, BulkFlyoutMode, MessageKey).
• Net: 17 files changed, +5/-379 lines. No behavior change — every removed symbol had zero cross-file references.

Test plan

• pnpm typecheck — no errors
• pnpm test — 42 files / 419 tests pass
• pnpm build — production build succeeds
• Grepped each of the 34 removed symbols — 0 references remain

---

Summary by cubic

Removed unused effect SubscriptionRef/Stream layers from queue, selection, toast, and checkbox-portal stores, plus dead helpers/types/icons across bulk-edit/duplicate/actions and lib. No behavior change; stores keep the callback subscribe() API, and the selection snapshot accessor remains.

• Refactors
  • Removed stream mirrors from queueStore, selectionStore, toastStore, and checkboxPortalStore; kept the synchronous selection snapshot accessor.
  • Deleted src/lib/store-streams.test.ts.
  • Removed unused helpers/exports (examples: SEARCH_OWNER_REPOS, sprintProgress, SecondaryAction, CircleCheckIcon, UnpinIcon, disposeRuntime, DistributionFunction, BulkFlyoutMode, MessageKey).
  • Net: +5 / -379 across 17 files.

^{Written for commit c0831bc. Summary will update on new commits.}

[github-actions]

Cursor auto review

No actionable issues found on changed lines.

No actionable issues found.

Generated automatically when this PR was submitted using Cursor CLI with --model auto.

[cubic-dev-ai]

No issues found across 17 files

_{Re-trigger cubic}

[cursor]

Risk: low. Cursor Bugbot was not configured on this PR; cubic and Cursor auto review reported no issues. Approved — dead-code removal with no behavior change and limited blast radius.

  

_{Sent by Cursor Approval Agent: Pull Request Approver}