feat: comprehensive registry improvements

Community docs:
- CODE_OF_CONDUCT.md (Contributor Covenant v2.1)
- SECURITY.md (vulnerability reporting policy)
- CHANGELOG.md (initial release notes)
- CODEOWNERS (per-type review ownership)

GitHub config:
- Issue templates: bug-report, pricing-correction, documentation
- FUNDING.yml (GitHub Sponsors)

Validation enhancements:
- Cross-reference check: hand [[requires]] → integration existence
- Routing alias collisions as warnings (errors with --strict)
- --strict flag to promote warnings to errors
- --type filter to validate single content type
- CI: add taplo format check and lychee link check jobs

Developer experience:
- Makefile with validate, fmt, and scaffold targets
- Scaffold templates for all 5 content types
- .pre-commit-config.yaml (trailing whitespace, TOML check, validate)
- docs/content-guide.md (naming, descriptions, prompts, decision guide)

Content quality:
- schema.toml: add last_verified field for model pricing
- CONTRIBUTING.md: add pricing verification guide with source links

.github/workflows/validate.yml

@@ -18,3 +18,30 @@ jobs:
 
       - name: Validate registry
         run: python scripts/validate.py
+
+  toml-format-check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+
+      - name: Install taplo
+        run: |
+          curl -fsSL https://github.com/tamasfe/taplo/releases/latest/download/taplo-full-linux-x86_64.gz \
+            | gunzip > /usr/local/bin/taplo
+          chmod +x /usr/local/bin/taplo
+
+      - name: Check TOML formatting
+        continue-on-error: true
+        run: taplo fmt --check **/*.toml
+
+  markdown-link-check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+
+      - name: Check markdown links
+        uses: lycheeverse/lychee-action@v2
+        with:
+          args: --verbose --no-progress '**/*.md'
+          fail: false
+        continue-on-error: true