feat: docs generator and auto-sync for docs.mymir.dev

[FrkAk]

Summary

Task Reference: none (docs tooling, not tracked as a Mymir task)

Adds the generator that produces the docs.mymir.dev reference content from this repo's source of truth, plus the workflow that keeps it in sync.

• Extracts the 6 MCP tool input schemas, DESCRIPTIONS, and LIMITS into a standalone lib/mcp/schemas.ts so the generator can import them without pulling in the data layer. MCP server runtime is unchanged: the schemas and descriptions moved byte-identical.
• Adds scripts/generate-docs.ts (bun run docs:gen): renders the 6 tool pages from the live Zod schemas, syncs the 4 mymir skill references, and builds a skills/agents catalog from plugin frontmatter. Prose em/en-dashes in the output are normalized fence-aware.
• Adds .github/workflows/docs-sync.yml: on push to main touching lib/mcp/**, lib/graph/tool-handlers.ts, plugins/claude-code/**, or the generator, it regenerates and opens a PR against the docs repo.
• Adds a "Docs impact" section to this PR template.

Type of change

• Bug fix
• New feature
• Refactor / cleanup
• Documentation

Testing

• bun test tests/scripts tests/plugins tests/api passes (122 tests)
• Linting passes (bun run lint)
• Typecheck passes (bun run typecheck)
• bun run check:plugins reports in sync
• bun run docs:gen regenerates with no unexpected diff

Notes for reviewer

• The lib/mcp/schemas.ts extraction is behavior-preserving: every schema field and .describe() string moved verbatim; tests/plugins and tests/api cover the unchanged MCP server.
• docs-sync.yml needs a DOCS_REPO_TOKEN secret (fine-grained PAT, Contents + Pull requests: read/write) before it can open sync PRs.
• references/artifacts.md and its three platform mirrors changed only to wrap banned-word examples in backticks, so the generated docs pass the style lint; check:plugins stays green.