feat(docs): complete P2.6 type safety cleanup and P2.7 system invariants

P2.6: Type Safety Cleanup
- Replaced 'any' return types in vite-plugin.ts with concrete types (UserConfig, transform return type)
- Documented TypeScript mixin 'any[]' exception in PlatformServiceMixin.ts
- Audit confirmed: zero 'any' in codebase except documented TS mixin limitation
- All external boundaries use 'unknown', all data payloads use 'Record<string, unknown>'

P2.7: System Invariants Documentation
- Created SYSTEM_INVARIANTS.md documenting all 6 enforced invariants
- Added to docs/00-INDEX.md under Policy & Contracts section
- Each invariant includes: What, Why, How, Where

Progress Docs Updates:
- Updated 00-STATUS.md: marked P2.6/P2.7 complete, added type safety invariant note
- Updated 01-CHANGELOG-WORK.md: added 2025-12-22 entries for P2.6/P2.7
- Updated 03-TEST-RUNS.md: added P2.6 type safety audit test run
- Updated P2-DESIGN.md: marked P2.6 acceptance criteria complete
- Updated SYSTEM_INVARIANTS.md: added Type Safety Notes section

Baseline Tag:
- Created v1.0.11-p0-p1.4-p1.5-p2.6-p2.7-complete

TypeScript compilation: ✅ PASSES
Build: ✅ PASSES
CI: ✅ All checks pass

docs/testing/QUICK_REFERENCE.md

@@ -1,5 +1,7 @@
 # DailyNotification Testing Quick Reference
 
+> **Note:** For P0 production-grade features testing, see [QUICK_REFERENCE_V2.md](./QUICK_REFERENCE_V2.md)
+
 ## 🚀 Quick Start
 
 ### Manual Testing

docs/testing/QUICK_REFERENCE_V2.md

@@ -1,5 +1,7 @@
 # Testing Quick Reference - P0 Production-Grade Features
 
+> **Note:** For general testing commands, see [QUICK_REFERENCE.md](./QUICK_REFERENCE.md)
+
 ## Current Version Features
 
 ✅ **P0 Priority 1**: Channel Management (ChannelManager)