feat: implement repository clone mode with SSH key support

- Add clone_mode and branch fields to tool_instances
- Add ssh_key_id to git_repositories for per-repo SSH key assignment
- Implement host-side git cloning with branch selection (default: main)
- Mount SSH keys into containers for git operations in clone mode
- Add dirty state check on clone-mode instance deletion with confirmation
- Update SessionsPage with mount/clone selector, branch input, SSH key display
- Add SSH key selector to repository creation form
- Add dirty delete confirmation modal with changed files list
- Update API schemas and endpoints for new fields
- Sync delta specs to main specs (git-repo, tool-instances, repo-clone-mode)
- Archive completed OpenSpec change: repo-clone-mode-with-ssh
- Document git requirement for custom tool types

Quality gates: Frontend typecheck and build passed
OpenSpec: repo-clone-mode-with-ssh archived with all tasks complete

apps/api/alembic/versions/2026_05_22_add_clone_mode.py

@@ -0,0 +1,36 @@
+"""add_clone_mode_and_ssh_key_id
+
+Revision ID: 2026_05_22_add_clone_mode
+Revises: 0014_merge_heads
+Create Date: 2026-05-22 20:30:00.000000
+"""
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision = '2026_05_22_add_clone_mode'
+down_revision = '0014_merge_heads'
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # Add ssh_key_id to git_repositories
+    op.add_column('git_repositories', sa.Column('ssh_key_id', postgresql.UUID(), nullable=True))
+    op.create_foreign_key('fk_git_repositories_ssh_key', 'git_repositories', 'ssh_keys', ['ssh_key_id'], ['id'])
+    
+    # Add clone_mode and branch to tool_instances
+    op.add_column('tool_instances', sa.Column('clone_mode', sa.String(20), nullable=False, server_default='mount'))
+    op.add_column('tool_instances', sa.Column('branch', sa.String(255), nullable=True, server_default='main'))
+
+
+def downgrade() -> None:
+    # Drop columns from tool_instances
+    op.drop_column('tool_instances', 'branch')
+    op.drop_column('tool_instances', 'clone_mode')
+    
+    # Drop ssh_key_id from git_repositories
+    op.drop_constraint('fk_git_repositories_ssh_key', 'git_repositories', type_='foreignkey')
+    op.drop_column('git_repositories', 'ssh_key_id')