Sprint 131: Sprint 129 Seed Closure + Minor Maintenance

Decisions

Context: Seed 1 identified in Sprint 129 Critic 1st review. TopNav.tsx (392 lines) is completely dead code with 0 production imports since AppLayout was introduced. TopNav.test.tsx (551 lines) is also dead code.
Choice: Delete TopNav.tsx + TopNav.test.tsx + replace 5 @related TopNav comments with AppLayout references (LanguageSwitcher, StudySidebar, avatars.ts, study-room/page.tsx)
Verification: Confirmed 0 remaining references via grep -rn "TopNav" frontend/src/
Code Paths: Deleted — frontend/src/components/layout/TopNav.tsx, frontend/src/components/layout/__tests__/TopNav.test.tsx
PR: #159 (411479b)

Context: Seed 2 identified in Sprint 129 Critic 1st review. L189-196 Case 1 ("dashboard nav is active on locale-stripped /dashboard path") and L198-203 Case 2 ("dashboard nav activated on Korean locale /dashboard — regression") have identical behavior: both use mockUsePathname.mockReturnValue('/dashboard') + bg-primary-soft assertion.
Choice: Preserve Case 1 (clearly expresses locale-stripped meaning), delete Case 2 (-6 lines)
Code Paths: frontend/src/components/layout/__tests__/AppLayout.test.tsx L198-203 deleted
PR: #159 (411479b)

Context: Prevention of Sprint 130 ADR-026 G1 (sprint number confusion due to missing memory window update). During Sprint 125~130, sprint-window.md was stuck at Sprint 92, causing PR/branch naming contamination with sprint-93.
Choice: Added step 2.5 to /start skill — compares the latest ADR number in docs/adr/sprints/ with the sprint-window.md [2] number within a ±2 range, outputs a warning if mismatched.
Note: .claude/ directory is included in .gitignore, so only local application is possible. Git tracking not available.

Item	Value
Total changes	-955 lines (5 insertions, 955 deletions)
jest	1356 passing (1408 → 1356, -52 tests: TopNav 51 + duplicate 1)
tsc	clean
lint	clean
CI	30+ checks all SUCCESS
Critic	Codex gpt-5.4 session `019dc4a9-5025-7262-baec-d0f4caa83885` — ready to merge ✅
PR	#159 Squash merge `411479b`
Commits	1 (squash)
end_commit	`411479b`

Remaining unprocessed items from Sprint 130 carryover (6 items):