Show app versions in launch-button tooltips

[ClaudiuSchuster]

What changed

• Show the installed ChatGPT package/version and Codex CLI version in the two launch-button tooltips.
• Add the known release date only for the exact detected versions, separated with an em dash.
• Keep missing and unreadable installations clear with not installed and version unavailable.
• Keep the 420 ms delay and centered, above-pointer positioning limited to these two button tooltips.

Security and privacy impact

No change to authentication, analytics, account data, or persisted settings. The applet reads local executable version output synchronously and displays it locally; no credentials or private paths are included.

Verification

• make verify
• Added regression coverage for installed, missing, unreadable, dated, and unknown-version tooltip states.
• Validated both button tooltips in the real Cinnamon/X11 applet, including above-pointer placement, horizontal centering, monitor bounds, and horizontal-panel orientation.
• No credentials, tokens, private paths, account-specific details, or screenshots were added.
• Live deployment reloaded through the normal installer: 10/10 managed files match, 0 symlinks, 0 mismatches.