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/integration.toml

@@ -0,0 +1,29 @@
+id = "{{NAME}}"
+name = "TODO: Service Display Name"
+description = "TODO: One-sentence description of this integration."
+category = "devtools"  # devtools | communication | storage | monitoring | data | productivity
+icon = "TODO"
+tags = ["TODO"]
+
+[transport]
+type = "stdio"
+command = "npx"
+args = ["-y", "TODO: @scope/mcp-server-package"]
+
+[[required_env]]
+name = "TODO_API_KEY"
+label = "TODO: API Key"
+help = "TODO: How to obtain this key"
+is_secret = true
+get_url = "https://example.com/settings"
+
+[health_check]
+interval_secs = 60
+unhealthy_threshold = 3
+
+setup_instructions = """
+TODO: Step-by-step setup instructions.
+1. Go to ...
+2. Create an API key with ...
+3. Paste the key above.
+"""