## Why

Config profiles currently only support inline file content, which is impractical for dotfiles and configuration repositories that users manage with git. Users need a way to include files from git repositories (similar to yadm) so they can version-control their dotfiles and mount them into containers at startup.

## What Changes

- Add `git_mounts` field to config profiles, allowing references to git repositories
- Mount specific paths from git repositories into containers at configurable target paths
- Support branch/tag selection for reproducible mounts
- Integrate with existing profile resolution and instance startup pipeline
- Update config profile UI to manage git repository mounts alongside existing mounts
- **No breaking changes** - existing profiles continue to work unchanged

## Capabilities

### New Capabilities
- `config-profile-git-mounts`: Mounting files from git repositories into containers via config profiles, including repo selection, path mapping, and branch pinning

### Modified Capabilities
- `tool-instances`: Instance startup pipeline now processes git mounts from resolved profiles before container creation
- `git-repo`: Repository model may need branch/tag listing for mount configuration

## Impact

- **Backend**: `apps/api/src/models/config_profile.py` - add git_mounts field
- **Backend**: `apps/api/src/services/config_profile_resolver.py` - resolve git mounts in profile resolution
- **Backend**: `apps/api/src/services/docker.py` or instance startup - bind mount from repo path to container
- **Backend**: `apps/api/src/api/config_profiles.py` - CRUD for git mounts
- **Frontend**: `apps/web/src/pages/config-profiles.tsx` - UI for managing git mounts
- **Frontend**: `apps/web/src/api/config_profiles.ts` - API types for git mounts
- **Database**: Migration to add git_mounts column to config_profiles table
