fix(auv-api-proto): vendor schemas for Cargo Git installs

[nekomeowww]

cargo install --git https://github.com/moeru-ai/auv auv-cli --bin auv failed because auv-api-proto imports google/api/annotations.proto from an ignored proto/vendor/ directory. CI generated that directory before compiling, hiding the incomplete Git checkout.

Check in the existing lockfile-pinned BSR export (47 schemas), including upstream license and documentation files via buf export --all. Rust, JS CLI, and release builds now consume the checked-in files directly. A separate Linux/Windows CI job regenerates the export and rejects modified, missing, or untracked files. Vendor files use LF and are marked as vendored for GitHub diffs.

Validation on macOS arm64:

• Reproduced the missing import from tracked Git sources; the fixed snapshot compiled all first-party schemas, and removing annotations.proto reproduced the failure again.
• Installed from an isolated local Git snapshot with cargo install --git file://<snapshot> --rev <commit> auv-cli --bin auv --locked --root <temporary-install> --target-dir <build-cache> in the default release profile, without generating dependencies in Cargo's checkout. Reused the original failed-install build cache.
• Installed auv --help and auv invoke --help passed.
• cargo test -p auv-api-proto --locked: 3 passed.
• Dependency regeneration produced no differences; cargo fmt --check, shell syntax, workflow YAML parsing, and whitespace checks passed.

Linux/Windows execution, including PowerShell regeneration, remains for CI. Registry crate packaging is outside this Git-install fix.

Dependency maintenance and verification reference