Remove prototype UI clutter and add a Tools keybindings view

Remove screenshot-identified passive sidebar/footer hints (save status, session-lifetime hint, engine branding and shortcut strip), inline-image diagnostic entry points, and About this prototype. Add a native read-only Keybindings view under Tools covering actual workspace and terminal shortcuts. Keep actionable errors, destructive confirmations, inline-image terminal support and regression probes. Preserve existing saved image-probe pane identities/reattachment; stopped legacy probe panes should offer a fresh shell, not rerun diagnostics. No protocol/dependency changes, active window/service restart, user-state reuse, commits or push. Acceptance: clean normal/minimum-size workspace without the requested clutter; Tools opens a readable, keyboard-dismissible keybindings reference matching active shortcuts; diagnostics are no longer launchable as built-in app features; legacy layouts remain safe; existing backend and private virtual-KWin UI regressions pass, with new targeted coverage and visual inspection. Implementation: removed passive sidebar/footer content, prototype dialog, menu/CLI image-probe launch and built-in images kind launch; retained legacy layout decoding and mapped explicit stopped starts to shells without changing identities. Shared Keybindings.qml supplies workspace/terminal sequences and the Tools reference; closing restores focused pane input. Image regression tests now launch their fixture explicitly. New legacy-start regression failed against original implementation and passes with the fix. Build and all seven backend suites pass. Private virtual-KWin suite passes 18 rows including both minimum/normal keybindings references, Escape/focus/new-tab shortcut and image/lifecycle regressions. The initial native failure was a QObject-vs-visual-tree test lookup, corrected to inspect the dialog content tree. Final validation: ./scripts/build.sh passes without compiler warning/error matches; all seven CTest suites pass, including executable rejection/help omission of --image-check and legacy stopped-probe shell recovery. Final private virtual-KWin native suite passes all 18 rows (no failures/skips); normal/minimum-size clean-workspace and padded keybindings captures visually inspected. One combined build/backend/native command hit its local 120-second budget after backend success; no runner remained, and a fresh standalone native run completed successfully in about 19 seconds. Final diff/whitespace inspection passes. Active window/service and real user state remain untouched. No commits or push.