feat: config profile multi-repo mounts

- Add mappings array support to git_mount entries
- Clone repository once per git_mount entry, mount multiple subdirectories
- Normalize legacy source_path+target_path to mappings on read
- Update _merge_git_mounts to dedup by (remote_url, branch) and concatenate mappings
- Add _normalize_git_mount, _clone_git_repo, _resolve_git_mount_mappings helpers
- Update GitMountItem Pydantic model with GitMountMapping and model_validator
- Update frontend GitMountEditor component with mappings UI
- Auto-convert legacy git mount entries to mappings format on load
- Add 15 backend unit tests for normalization, resolution, and glob expansion
- Update existing config profile resolver tests for new merge behavior

Quality gates: pytest 167 passed, frontend typecheck clean

Addresses: config-profile-multi-repo-mounts

apps/api/src/services/config_profile_resolver.py

@@ -176,21 +176,59 @@ def _merge_git_mounts(
 ) -> list[dict[str, Any]]:
     """Merge git mounts from included profiles.
 
-    Later mounts override earlier ones with the same remote_url + target_path combo.
+    Entries with the same remote_url + branch have their mappings concatenated.
+    Different repos are kept as separate entries.
+    All entries are normalized to the mappings format.
     """
     result = list(base)
-    # Build lookup by (remote_url, target_path)
-    seen = {(m["remote_url"], m["target_path"]): i for i, m in enumerate(result)}
+    # Normalize existing entries to mappings format
+    for i, m in enumerate(result):
+        result[i] = _normalize_git_mount_entry(dict(m))
+
+    # Build lookup by (remote_url, branch)
+    seen = {}
+    for i, m in enumerate(result):
+        key = (m["remote_url"], m.get("branch"))
+        seen[key] = i
+
     for mount in overlay:
-        key = (mount["remote_url"], mount["target_path"])
+        mount = _normalize_git_mount_entry(dict(mount))
+        key = (mount["remote_url"], mount.get("branch"))
         if key in seen:
-            result[seen[key]] = dict(mount)
+            # Same repo+branch: concatenate mappings, dedup by (source_path, target_path)
+            existing = result[seen[key]]
+            existing_sources = {
+                (m["source_path"], m["target_path"])
+                for m in existing.get("mappings", [])
+            }
+            for mapping in mount.get("mappings", []):
+                map_key = (mapping["source_path"], mapping["target_path"])
+                if map_key not in existing_sources:
+                    existing["mappings"].append(dict(mapping))
+                    existing_sources.add(map_key)
         else:
             seen[key] = len(result)
-            result.append(dict(mount))
+            result.append(mount)
     return result
 
 
+def _normalize_git_mount_entry(entry: dict[str, Any]) -> dict[str, Any]:
+    """Normalize a git mount entry to the unified mappings format.
+
+    Converts legacy source_path + target_path into a single-entry mappings array.
+    """
+    entry = dict(entry)
+    if "mappings" not in entry or not entry.get("mappings"):
+        source = entry.get("source_path", ".")
+        target = entry.get("target_path")
+        if target is not None:
+            entry["mappings"] = [{"source_path": source, "target_path": target}]
+    # Remove legacy fields once normalized
+    entry.pop("source_path", None)
+    entry.pop("target_path", None)
+    return entry
+
+
 async def _resolve_profile_recursive(
     session: AsyncSession,
     profile_id: uuid.UUID,