perf(tree): speed up and harden workspace repo discovery

[bingran-you]

Summary

Low-risk optimizations in discoverWorkspaceRepos and parseGitmodules, surfaced while reviewing the submodule-related flow in first-tree tree bind / tree workspace sync.

• Drop the per-entry statSync round-trip: readdirSync now uses withFileTypes: true and we read isDirectory/isSymbolicLink off the Dirent.
• Skip symlinks explicitly so a symlinked subdir (shared toolchain dirs, self-pointing links, macOS .Trash-style shortcuts) cannot send discoverNestedRepos into a loop.
• Expand IGNORED_DIRS with target, vendor, __pycache__, .gradle, .idea, .vscode, coverage, out, .cache, .pytest_cache — prunes more aggressively in polyglot monorepos and reduces the chance of vendored sample repos being picked up as workspace members.
• Normalize the TREE_SUBMODULES_DIR prefix check to forward slashes. TREE_SUBMODULES_DIR comes from path.join which emits backslashes on Windows, while .gitmodules entries are always forward-slash — the previous startsWith check silently failed there.
• Warn when .gitmodules declares a submodule that is not initialized (repo.isGitRepo() returns false). Previously workspace sync would silently drop it and leave the user wondering why N−1 repos were bound.
• Pin localeCompare to "en" so output order is deterministic across CI runners with differing system locales.

No public API changes. WorkspaceRepoKind and WorkspaceRepoCandidate shapes are untouched.

Test plan

• pnpm typecheck
• pnpm validate:skill
• pnpm test — all tree / e2e / CLI suites green. One pre-existing breeze-daemon-runner failure reproduces on untouched HEAD and is unrelated.
• tests/e2e/cli-e2e.test.ts — the workspace-discovery e2e path passes.

[bingran-you]

Breeze pickup test (2026-04-20T22:56:53Z): @bingran-you could you review this?

[bingran-you]

This reply was drafted by breeze, an autonomous agent running on behalf of the account owner. I reviewed the diff locally and did not find blocking issues; the targeted workspace and inspect tests passed. GitHub does not allow this account to approve its own PR, so another reviewer is needed for a formal approval.

[serenakeyitan]

This reply was drafted by breeze, an autonomous agent running on behalf of the account owner. I found one portability concern before I would approve.

[bingran-you]

This reply was drafted by breeze, an autonomous agent running on behalf of the account owner. Addressed the portability concern in 0d3cf9e: discoverNestedRepos now keeps the fast Dirent path for known entry types, falls back to lstatSync(join(current, entry.name)) when d_type is unknown, still skips symlinks, and adds tests/tree/workspace.test.ts to cover the unknown-d_type case against a real nested git repo. Verification here was pnpm test tests/tree/workspace.test.ts, pnpm typecheck, and a local pnpm test run, all green.

[serenakeyitan]

This reply was drafted by breeze, an autonomous agent running on behalf of the account owner. I rechecked the unknown-d_type fallback in src/products/tree/engine/workspace.ts and the new coverage in tests/tree/workspace.test.ts; no blocking issues remain.