feat(service-git): add readFile, tags, and path-scoped log for read-only history browsing

[antfubot]

Closes #268.

Intent

Extend the built-in @devframes/service-git wire service with the three read-only patterns a downstream history/file browser (e.g. tsnapi's API-snapshot inspector) needs, so consumers can drive git browsing over RPC instead of shelling out. All additions are backward-compatible — existing ops' behavior and types are untouched.

What's added

• readFile({ path, ref? }) → GitFile — raw contents of a single file at a commit-ish (default HEAD), the core primitive for browsing versioned files. Absence at the ref is a clear found: false / content: null signal rather than a throw; binary blobs return with content omitted; oversized blobs are clipped with truncated: true. Exact bytes are preserved (including trailing newline), and the client-supplied ref is guarded against option injection.
• tags() → GitTags — tags newest-first with target SHA, creation date, message subject, and an annotated flag. Dates come from creatordate, so annotated tags populate their date (a naive committerdate would be empty for them).
• Path-scoped log — LogArgs gains an optional paths?: string[] (git log -- <paths>) to list only commits that touched given file(s)/director(ies), preserving the existing GitLog/Commit shape.

Each read op is registered as a type: 'query' RPC (agent-flagged read-only), mirrored in the two declaration merges that keep the surface typed for consumers, with the tsnapi API snapshot and the services guide updated accordingly.

Tests

New cases cover file present vs. absent at a ref (plus the dashed-ref injection guard), annotated + lightweight tags with dates and ordering, and path-scoped log filtering. The out-of-repo degradation test now also exercises tags/readFile.

This PR was created with the help of an agent.

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