feat(mcp): register a gittensory://finding-taxonomy resource enumerating review finding categories

[JSONbored]

The hosted MCP server (src/mcp/server.ts) registers zero resources, and there is no machine-readable enumeration of the review finding-category taxonomy that #1958 (part of #1953) is adding to AI findings (security/correctness/performance/maintainability/tests/style). Expose a read-only MCP resource so agents can discover the canonical category enum + severities without hard-coding them. (Resource only — do NOT change the finding schema; that's #1958.)

Deliverables

• Add server.registerResource(...) support in src/mcp/server.ts (currently none exist) with URI gittensory://finding-taxonomy, mimeType application/json
• Return the canonical category enum + severity levels as a static JSON document; source the constant from a single shared const so it stays in sync with the finding schema
• Tests: resource read returns the expected JSON and every category/severity value is present

References

• src/mcp/server.ts:1067
• src/review/stats.ts:45
• src/review/auto-tune.ts:252

Part of #1958.

---

size: S · held for later release (gittensor:feature once activated)

[linear-code]

JSO-2326