feat(control): expose running app identity for computer-use attachment #801

The MCP listed stable windows but did not connect them to a native computer-use application identity. In this development setup the packaged Agent Code app was stopped, one Electron app was running, and multiple checkouts exposed Electron bundles with the same bundle ID. Both native Window menu entries were Agent Code.

The operator guessed a worktree Electron executable and accidentally opened a blank launcher. This was an operator launch mistake, not an extra window created by Agent Code. Attaching to the actual running checkout resolved it. The user explicitly wanted existing windows only.

Expected/acceptance: expose non-secret PID, actual app bundle/executable path and development/packaged identity where supported; provide distinguishable window descriptions and an attach-to-existing-process recipe; handle multiple checkouts sharing Electron identity. Keep stable MCP window IDs/generations authoritative.

Impact: unexpected launcher window, confusion and recovery during setup. Related #688.

Environment: macOS, development Electron, two Agent Code windows, external MCP plus computer use, observed 2026-09-05. Exact running build revision was not verified. Refs #793, #795.