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

templates/provider.toml

@@ -0,0 +1,22 @@
+# TODO: Provider Name — https://example.com
+# Models: 1
+
+[provider]
+id = "{{NAME}}"
+display_name = "TODO: Provider Display Name"
+api_key_env = "TODO_API_KEY"
+base_url = "https://api.example.com/v1"
+key_required = true
+
+[[models]]
+id = "TODO-model-id"
+display_name = "TODO: Model Display Name"
+tier = "balanced"  # frontier | smart | balanced | fast | local
+context_window = 128000
+max_output_tokens = 4096
+input_cost_per_m = 0.0
+output_cost_per_m = 0.0
+supports_tools = true
+supports_vision = false
+supports_streaming = true
+aliases = []