feat(mcp): gittensory_validate_config tool for .gittensory.yml

[JSONbored]

Add an MCP tool that parses a supplied .gittensory.yml string and returns the normalized config + every warning, so contributors/operators can pre-validate a manifest before pushing (a pre-submit predictor, sibling of the existing MCP predictors). Supports the #1683 generator's requirement that dashboard/YAML validate against the SAME parser.

Deliverables

• Add a gittensory_validate_config tool in the MCP surface (packages/gittensory-mcp/** + src/mcp/**) that calls parseFocusManifest on the input and returns { normalized, warnings, present }
• Reuse the existing parser as the single source of truth (no parallel schema)
• Unit tests: valid config, config with warnings, malformed YAML; branch coverage on the ok/warn/error arms
• Document the tool in the MCP tool reference

References

• src/mcp/
• packages/gittensory-mcp/
• src/signals/focus-manifest.ts:1013 (parseFocusManifest reused)
• part of #1683 (epic #1680)

Part of #1683.

---

size: M · gittensor:feature

[linear-code]

JSO-2174