feat: Add path scoping to rules and enforce project init workflow

- Add paths frontmatter to frontend, backend, and security rules so
  they only load when editing relevant files
- Add mandatory new-project detection to general rules that redirects
  to /requirements before any implementation
- Add write-then-verify protocol for feature tracking updates to
  prevent hallucinated file edits

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

.claude/rules/backend.md

@@ -1,3 +1,10 @@
+---
+paths:
+  - "src/app/api/**"
+  - "src/lib/supabase*"
+  - "supabase/**"
+---
+
 # Backend Development Rules
 
 ## Database (Supabase)