fix: limit recursive file watcher usage

[oz-for-oss]

Closes #7205

Summary

• Replaced project-scoped file-based MCP recursive repo watching with non-recursive watches on known config parent directories.
• Applied repository ignore filtering when registering recursive repository watchers so ignored trees do not consume watcher budget.
• Added unit coverage for MCP config path bookkeeping.

Validation

• cargo fmt --manifest-path /workspace/warp/Cargo.toml --all
• CARGO_BUILD_JOBS=1 cargo test --manifest-path /workspace/warp/Cargo.toml -p repo_metadata --features local_fs
• CARGO_BUILD_JOBS=1 cargo check --manifest-path /workspace/warp/Cargo.toml -p warp --features local_fs --lib
• CARGO_BUILD_JOBS=1 cargo clippy --manifest-path /workspace/warp/Cargo.toml -p repo_metadata -p warp --features local_fs --all-targets -- -D warnings

Notes

• The warp lib test harness for file_mcp_watcher_tests was attempted twice with single-job compilation, but the sandbox killed rustc with SIGKILL before tests could run.