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/ISSUE_TEMPLATE/pricing-correction.yml

@@ -0,0 +1,44 @@
+name: Pricing Correction
+description: Report outdated or incorrect model pricing
+labels: ["pricing"]
+body:
+  - type: input
+    id: provider
+    attributes:
+      label: Provider Name
+      description: Which provider's pricing needs correction?
+      placeholder: e.g. openai, anthropic, groq
+    validations:
+      required: true
+
+  - type: input
+    id: model_id
+    attributes:
+      label: Model ID
+      description: The canonical model identifier.
+      placeholder: e.g. gpt-4o, claude-sonnet-4-20250514
+    validations:
+      required: true
+
+  - type: input
+    id: current_pricing
+    attributes:
+      label: Current Pricing in Registry
+      description: What does the registry currently show?
+      placeholder: "e.g. Input: $5.00 / 1M tokens, Output: $15.00 / 1M tokens"
+    validations:
+      required: true
+
+  - type: textarea
+    id: correct_pricing
+    attributes:
+      label: Correct Pricing (with source)
+      description: |
+        Provide the correct pricing and a link to the official source
+        so we can verify the update.
+      placeholder: |
+        Input: $2.50 / 1M tokens
+        Output: $10.00 / 1M tokens
+        Source: https://openai.com/pricing
+    validations:
+      required: true