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/web/src/api/config_profiles.ts

@@ -24,11 +24,18 @@ export interface ConfigProfileMount {
   files: Record<string, string>;
 }
 
-export interface GitMount {
-  remote_url: string;
+export interface GitMountMapping {
   source_path: string;
   target_path: string;
+}
+
+export interface GitMount {
+  remote_url: string;
   branch?: string;
+  mappings: GitMountMapping[];
+  // Legacy fields (for backward compatibility when reading old data)
+  source_path?: string;
+  target_path?: string;
 }
 
 export interface ConfigProfileInclude {