feat(connections): open a connection in a dedicated window

[debba]

Overview

Adds an "Open in New Window" action to the connection context menus (the open-connections sidebar rail and the Connections page) that opens a connection in its own standalone window, together with the cross-window plumbing needed to keep connection state consistent across every window.

Behaviour

Opening

• Validate before spawning. The connection is test_connection'd first; the window is created only if the connection succeeds. A failing connection now surfaces the error in the originating window (with a spinner on the card while validating) instead of opening an empty window that then errors.
• If the connection is already open somewhere, validation is skipped — the window is opened (or an existing one is focused) directly.

Ownership & sidebar

• A connection opened in a new window is "owned" by that window and is detached from the originating window's sidebar rail. The process-global pool stays warm and is reused by the new window (no reconnect round-trip).

Cross-window state sync

• Connection open-state is now shared across all windows: a connection open in any window shows as open in every window's Connections page (badge, card styling, connect/disconnect action).
• Implemented on top of the existing health-check active-connection registry, broadcast via a new connections:active-changed event and seeded on window start via get_active_connections.

Lifecycle

• Disconnecting a connection closes its dedicated window — from anywhere. The main window is never auto-closed.
• Closing a dedicated window also tears down its bound connection, so nothing leaks.

Guards

• "Open in New Window" is disabled when the current window has no open connection.

Implementation

Backend (src-tauri/)

• connection_window.rs (new): open_connection_window command — creates/focuses a connection-window-<id> window loading /?connect=<id>; a CloseRequested handler disconnects the bound connection on close.
• capabilities/default.json: whitelist connection-window-*.
• health_check.rs: broadcast the active-connection set on register / disconnect / health-failure; add active_connections() + emit_active_changed().
• commands.rs: register_active_connection and disconnect_connection now emit the broadcast; new get_active_connections command.

Frontend (src/)

• New hooks: useOpenConnectionInNewWindow (validate → open → detach), useAutoConnectFromUrl (auto-connect the dedicated window on startup), useConnectionWindowLifecycle (close the dedicated window when its connection goes away).
• DatabaseProvider: globallyOpenConnectionIds + isConnectionOpenAnywhere, plus a detachConnection helper (removes from a window's UI without closing the pool).
• Connections page / cards: reflect global open-state; "Open in New Window" menu entry + disabled guard.
• i18n: sidebar.openInNewWindow added to all 8 locales.

Tests / cleanup

• Unit tests for useOpenConnectionInNewWindow, useAutoConnectFromUrl, useConnectionWindowLifecycle, and the Rust window-label sanitizer.
• Removed the now-unused hasConnectionMenuItems helper and its tests.

Verification

• npm run build (tsc -b + vite) — ✅
• npm run lint — ✅ 0 errors
• npx vitest run — ✅ 2706 passed
• cargo test — ✅ 770 passed
• cargo clippy --all-targets — ✅ 0 errors

Notes

• GitNexus MCP was not connected during development, so gitnexus_detect_changes / impact analysis could not be run; changes are largely additive.