Add agent control tools for GridBash panes

[jasonsuhari]

Problem

Manager agents need a small control surface for GridBash without broad automation yet.

Requested behavior

Add an opt-in local agent control path that can:

• show an image/artifact inside GridBash
• send command text to one or more panes
• set the GridBash status line

Acceptance checks

• Control API is off by default and enabled explicitly.
• MCP-facing tools exist for image display, pane command sending, and status updates.
• Pane command routing uses existing pane input behavior and avoids sleeping panes.
• Image display presents a clear in-app overlay from a local path.
• Fast Rust validation passes.

[jasonsuhari]

PR #81 is merged to main and local-main validation passed, but
pm run install:local is blocked by an active file lock on the installed executable. npm failed with EBUSY while copying C:\Users\Jason\AppData\Roaming\npm\node_modules\gridbash\npm\bin\win32-x64\gridbash.exe. Running GridBash processes were present at the time: 8552, 22188, 22780. Leaving this open until the local executable can be updated.