fix: filter gitignored directories from inotify recursive watches

[warp-dev-github-integration]

Description

Fix excessive memory usage (11+ GB) caused by inotify registering watches on gitignored directory trees (e.g. node_modules/, target/).

Root cause: repo_watch_filter() only pruned .git/ internal directories from the recursive walk, but did not skip gitignored directories. When watching a repository recursively on Linux, inotify creates a watch on every subdirectory. For projects with large ignored trees, the notify crate's internal HashMap<PathBuf, (WatchDescriptor, WatchMask, ...)> grew to ~3 GB from rehashing, and Vec<u8>::clone during rehashing consumed ~8 GB.

Heap profile evidence (Sentry event 82189ab726af469a990bbe20819b78ca):

• 11.23 GB total in-use
• 98.48% (11.05 GB) from notify::inotify::EventLoop::add_watch → add_single_watch
• 71.66% (8.04 GB) from Vec<u8>::clone (HashMap buffer rehashing)
• 26.73% (3 GB) from hashbrown::raw::RawTable::reserve_rehash

Fix:

1. Add repo_watch_filter_with_gitignores() that combines the existing .git/ filtering with gitignore-based directory pruning in the descend predicate. This follows the pattern already used by the codebase indexer (CodebaseIndexManager::watch_path).
2. Update DirectoryWatcher::start_watching_directory() and LocalRepoMetadataModel::add_repository_internal() to load root-level gitignore rules and use the new filter.
3. Fix FileModel::register_file_path() and fallback_to_individual_watchers() to use NonRecursive mode on the parent directory (matching open()'s existing correct behavior) instead of Recursive on the file path.

Linked Issue

• Sentry: https://sentry.io/organizations/warpdotdev/issues/7259255054/events/82189ab726af469a990bbe20819b78ca/

• Where appropriate, screenshots or a short video of the implementation are included below (especially for user-visible or UI changes).

Testing

• Verified cargo check and cargo clippy pass for repo_metadata and warp_files.
• The fix is structural: gitignored directories are pruned from the inotify recursive walk, preventing watch registration on those subtrees. This directly addresses the allocation sites shown in the heap profile.

Agent Mode

• Warp Agent Mode - This PR was created via Warp's AI Agent Mode

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