feat(vscode): index custom subfolders with multi-folder search and excludes

[talhaanwarch]

Summary

Adds three capabilities to the VSCode extension's Semantic Code Search panel so you can index specific subfolders of an open workspace rather than the whole root:

• Custom index path(s): Open VSCode at a parent folder but index only the subfolder(s) you name. Retrieval comes from the same scope.
• Multiple subpaths: Index several subfolders at once (e.g. backend, frontend/src). Search fans out across all indexed folders in parallel and merges results by score.
• Exclude folders: Glob patterns to skip nested directories inside indexed folders.

Two new panel fields drive this:

• Folder(s) to index — comma/newline-separated paths relative to the workspace root. Empty = whole workspace (unchanged default behavior).
• Exclude folders — glob patterns applied on top of the defaults.

node_modules was already ignored by default; this PR also adds venv and .venv to the core default ignore list.

Design

• One collection per indexed folder. Each folder is indexed independently (its own collection keyed by resolved path), so adding/removing a folder doesn't rebuild the others. Search runs one query per folder in parallel (Promise.all) and merges by score. Auto-sync is scoped to the indexed folders, not the workspace root.
• Folder inputs and the resolved indexed-path list are persisted in workspaceState, so the panel prefills and search/sync know what to target across reloads.
• Path resolution rejects any path that escapes the workspace root.
• Search results are tagged with their source folder and carry an absolute path, fixing file-open for results outside the workspace root.

Testing

• packages/core: build clean, 28 unit tests pass (incl. new default-ignore test).
• packages/vscode-extension: tsc --noEmit clean; 8 new unit tests for path/result helpers pass.
• Full pnpm build passes.
• Manually verified end-to-end against a local Milvus + Ollama setup: indexed two subfolders, confirmed node_modules/venv and unlisted folders are skipped, search results are folder-tagged, and clicking a result opens the correct file and line.

Screenshot

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