Fix git sync and add repo browser with path selection

- Fix discover_files: rel_path always computed (was stuck at '.' at root),
  include_path_match now uses relative path, 'return' changed to 'continue'
- Fix ingest_git_source: files were cloned but ingested from wrong path
  (docs/repo-id instead of data/repos/repo-id). Now stages filtered files
  into DOCS_PATH/library_id before calling ingest_library.
- Add browse_repo_tree() for interactive repo exploration
- Add POST /api/v1/sources/browse endpoint to backend
- Add /sources/browse proxy route to webui
- Rewrite sources.html: browse repo, expand/collapse tree, check paths to
  include, then save source and sync

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/main.py

@@ -22,7 +22,7 @@ from .db import (
     search_libraries,
     upsert_library,
 )
-from .git_source import ingest_git_source
+from .git_source import browse_repo_tree, clone_or_update_repo, ingest_git_source
 from .ingest import ingest_all, ingest_library
 from .search import get_library_docs, resolve_library_id, search_docs
 from .vector_store import delete_library_vectors, ensure_collection, get_client, get_collection_name
@@ -55,6 +55,11 @@ class GitSourceRequest(BaseModel):
     exclude_paths: Optional[list[str]] = None
 
 
+class BrowseRepoRequest(BaseModel):
+    repo_url: str = Field(..., min_length=1)
+    branch: str = "main"
+
+
 DOCUMENT_EXTENSIONS = {
     ".md",
     ".txt",
@@ -424,6 +429,26 @@ async def api_add_source(source: GitSourceRequest):
     return {"success": True, "created": created, "source": source_entry}
 
 
+@app.post("/api/v1/sources/browse")
+async def browse_repo_api(payload: BrowseRepoRequest):
+    """Shallow-clone a repo and return its directory tree for path selection."""
+    import hashlib
+
+    repo_hash = hashlib.md5(payload.repo_url.encode()).hexdigest()[:10]
+    repo_id = f"browse-{repo_hash}"
+    try:
+        clone_result = clone_or_update_repo(
+            repo_id=repo_id,
+            repo_url=payload.repo_url,
+            branch=payload.branch,
+        )
+        repo_path = Path(clone_result["repo_path"])
+        tree = browse_repo_tree(repo_path)
+        return {"success": True, "tree": tree, "repo_url": payload.repo_url, "branch": payload.branch}
+    except Exception as exc:
+        raise HTTPException(status_code=400, detail=str(exc))
+
+
 @app.post("/sources/sync")
 async def sync_sources_api(payload: Optional[SyncSourcesRequest] = None):
     source_data = await api_list_sources()