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

docs/content-guide.md

@@ -0,0 +1,50 @@
+# Content Guide
+
+Guidelines for contributing content to the LibreFang Registry.
+
+## Naming Conventions
+
+- Use **lowercase, hyphenated** names: `my-agent`, `web-scraper`, `code-reviewer`.
+- Agent/hand/skill directory names must match their `name`/`id` field in the TOML.
+- Provider and integration filenames must match their `id` field.
+
+## Writing Descriptions
+
+- Keep descriptions to **1-2 sentences**. Lead with a verb.
+- Good: "Analyzes pull requests and suggests improvements."
+- Bad: "This is an agent that can be used to analyze pull requests."
+
+## System Prompts (Agents & Hands)
+
+- Start with a clear role statement: "You are X, responsible for Y."
+- Include specific instructions on behavior, not vague aspirations.
+- Define what the agent should **not** do (scope boundaries).
+- List tools it should use and when.
+- Aim for **100-500 words** for agents, up to 1000 for complex hands.
+- Avoid repeating information already in the TOML metadata.
+
+## Agent vs Hand vs Skill
+
+| Type | Use When |
+|------|----------|
+| **Agent** | Conversational, general-purpose, stateless Q&A or analysis. |
+| **Hand** | Multi-step workflow requiring tools (shell, files, APIs). Has settings, dashboard, requirements. |
+| **Skill** | Single focused task with defined inputs/outputs. Prompt-only or a short script. |
+
+- If it needs `shell_exec` or external tools, it is probably a **hand**.
+- If it is a reusable prompt template with parameters, it is a **skill**.
+- If it is a conversational assistant for a domain, it is an **agent**.
+
+## Provider Entries
+
+- Include all models the provider offers that support chat completions.
+- Use accurate `input_cost_per_m` / `output_cost_per_m` (USD per million tokens).
+- Set `tier` honestly: `frontier` is reserved for the most capable models.
+- Always include `context_window` and `max_output_tokens` from official docs.
+
+## General Tips
+
+- Run `make validate` before submitting.
+- Run `make fmt` if you have taplo installed to keep TOML formatting consistent.
+- Check `schema.toml` for the full field reference.
+- Test scaffold output: `make new-agent NAME=test-agent`, verify, then delete.