MCP fix: pass --profile to discovery CLI calls and surface resolver failures in configure mcp

[asujithan]

Issue:

• ucode configure mcp printed ! Skipped external connections / Genie spaces / Databricks apps on workspaces where the Databricks CLI's DATABRICKS_HOST-only auth resolver returns an Invalid Token. The auth helpers already passed --profile, but list_databricks_connections, list_genie_spaces, and list_databricks_apps did not, so _discover_mcp_source swallowed the resulting RuntimeError as ! Skipped ….
• _resolve_mcp_selection returned None for any unresolvable picker pick and the caller silently continue'd, so dropped picks were invisible.
• The picker prints done whether or not anything was toggled, so an Enter-without-space submission on fresh state looked identical to a successful save.

Change:

• Threaded an optional profile through list_databricks_connections, list_genie_spaces, list_databricks_apps and their discover_* wrappers, injected via the existing _profile_args() helper; configure_mcp_command reads it from state and forwards it to all three discovery calls.
• Changed _resolve_mcp_selection to raise RuntimeError with a per-cause reason (missing app name, app not in discovered list, app has no MCP URL, missing Genie space id, missing external connection name, unrecognized prefix); configure_mcp_command prints ! Skipped MCP selection `: ` instead of dropping the pick.
• Added a ! No MCP servers selected. Press space to toggle an item, then enter to save. hint when the picker submits zero selections on fresh state.
• Added regression tests for --profile plumbing (tests/test_databricks.py, tests/test_mcp.py) and for each new warning/hint; updated existing monkeypatch stubs from lambda workspace: … to lambda workspace, profile=None: ….

Validation:
uv run pytest tests/test_databricks.py tests/test_mcp.py -q → 99 passed
uv run ruff check src/ucode/databricks.py src/ucode/mcp.py tests/test_databricks.py tests/test_mcp.py → passed
uv run pytest -q --ignore=tests/test_e2e.py --ignore=tests/test_e2e_user_agent.py → 552 passed
uv run ruff check . → passed
Manually verified on eng-ml-inference-team-ca-central-1: picker now shows external connections, Genie spaces, and Databricks apps (previously ! Skipped …); a toggled selection is written to ~/.ucode/state.json and shows up in claude mcp list; Enter-without-space on fresh state prints the new hint instead of a silent no-op.

fixes #58