feat(goal-loop): add the per-agent enable-goal-loop-mcp command for parity with TLDR and Goal #1006

From the post-merge audit of PRs #1003/#1005.

Motivation

Every sibling built-in MCP domain has a per-agent enable command (enable-tldr-mcp, enable-goal-mcp in src/renderer/src/features/workspace/commands/sessionCommands.ts), so a user can flip the domain for one agent from the palette without a reload round-trip through Settings. goal_loop has the Settings row and the per-session override plumbing (mcpDomains.ts resolves it from the shared lists), but no palette command — a parity gap users will notice ("how do I turn on the loop for just this agent?").

Intended behavior

• enable-goal-loop-mcp session-surface command mirroring enable-goal-mcp: toggles the per-agent built-in MCP override for goal_loop, triggers the same reload flow, described for the palette in the house style.
• Catalog governance baselines (132 → 133) and the feature reference's commandIds updated in the same change.

Acceptance criteria

• Command appears for agent panes, toggles the override, and round-trips through reload
• catalog.test.ts governance arithmetic updated deliberately
• featureReference commandIds includes it