[Fix] PWA polish: remove type lies, dead config, and edge-swipe dead zone

[samzong]

Summary

Bundle six independent P3 polish items for the PWA package: eliminate non-null assertion type lies, remove dead tsconfig configuration, add missing service worker cache header, establish IndexedDB migration path, and reduce edge-swipe dead zone width.

Type of change

• [Fix] bug fix

Why is this needed?

Each item individually is small but collectively they address: (1) two ! non-null assertions that lie to the type checker and mask potential runtime errors, (2) a dead @/* path alias that misleads contributors, (3) a missing sw.js cache header that relies on implicit browser behavior instead of explicit spec-compliant policy, (4) an IndexedDB upgrade callback with no version guard that will break on the first schema change, and (5) a 20px edge-swipe detector that creates an unnecessarily large tap dead zone.

What changed?

• stores/hooks.ts: Replace selector! with conditional overload dispatch (selector ? useStore(api, selector) : useStore(api)) in all three store hooks
• tsconfig.json: Remove unused baseUrl and paths entries
• public/_headers: Add /sw.js with Cache-Control: public, max-age=0, must-revalidate
• persistence/db.ts: Add oldVersion parameter to upgrade callback and wrap store creation in if (oldVersion < 1)
• platform/index.ts: Replace _gwResult! with local variable extraction and runtime invariant check
• views/DrawerLayout.tsx: Reduce edge-swipe detector width from 20px to 12px

Architecture impact

• Owning layer: renderer (PWA package)
• Cross-layer impact: none
• Invariants touched from docs/architecture-invariants.md: none
• Why those invariants remain protected: all changes are internal to the PWA package with no cross-layer or cross-package effects

Linked issues

N/A

Validation

• pnpm lint
• pnpm test
• pnpm build
• pnpm check:ui-contract
• Manual smoke test
• Not run

Commands, screenshots, or notes:

pnpm typecheck — passed
pnpm test — 157 tests passed (shared 6, pwa 59, desktop 92)
pnpm lint — passed
pnpm check:architecture — passed
pnpm check:ui-contract — passed

Screenshots or recordings

No UI changes beyond the edge-swipe detector width reduction (20px → 12px), which is invisible — it only affects the touch target area.

Release note

• No user-facing change. Release note is NONE.
• User-facing change. Release note is included below.

NONE

Checklist

• The PR title uses at least one approved prefix: [Feat], [Fix], [UI], [Docs], [Refactor], [Build], or [Chore]
• The summary explains both what changed and why
• Validation reflects the commands actually run for this PR
• Architecture impact is described and references any touched invariants
• Cross-layer changes are explicitly justified
• The release note block is accurate

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