Report ignored documents distinctly

[fa1k3]

Summary

• return a distinct excluded_by_ignore lookup result when a requested document matches a configured collection ignore rule
• surface that reason through the MCP get tool, qmd:// resource, and CLI qmd get instead of presenting it as a generic missing file
• route CLI qmd get through the shared document lookup path so missing/ignored paths no longer fall back to an unrelated same-basename file
• add regression tests for absolute-path, virtual-path, CLI ignored-path, and CLI missing-path lookups

Why

If a file is intentionally excluded by an ignore rule, get currently looks the same as a typo or stale path. Returning the matched collection/path/rule makes the failure actionable without scanning the index manually.

The CLI also had a separate fallback that matched only the last path component. A request like private/log.md could return a different indexed *log.md file. Reusing the shared lookup avoids that surprising cross-path fallback.

Tests

• bun test test/cli.test.ts --timeout 60000 --preload ./src/test-preload.ts
• npm run test:node -- test/cli.test.ts
• bun test test/store.test.ts test/mcp.test.ts --timeout 60000 --preload ./src/test-preload.ts
• npm run test:node -- test/store.test.ts test/mcp.test.ts
• bun run build
• npm run test:types