v0.25.10: Use your Codex CLI sign-in in T3 Code

Use your Codex CLI sign-in in T3 Code

Choosing Continue with ChatGPT in T3 Code switches Codex to T3 Code's own ChatGPT connection, which ignores the CLI's sign-in. Setup could then say Signed in while T3 Code said Not authenticated, with nothing on the page to explain why.

• The Codex row in Setup → Agents now says Not used by T3 Code and offers Use in T3 Code. It does the same as T3 Code's Use existing CLI and applies without a restart.
• The switch only happens when you ask for it, since you may have chosen T3 Code's connection on purpose. The row isn't flagged as needing attention.
• If the CLI isn't signed in, the switch is refused and nothing changes.
• Enablement, other keys, other Codex accounts and the saved connection stay as they are. Unlike T3 Code's button, this doesn't turn on a disabled provider.
• When an update is available, Update keeps the row's button and the switch moves to the row's menu.

Tested on T3 Code 0.1.6 with a CLI API key, not a ChatGPT login. Setup handles both the same way.

Verification

• Add a browser audit covering the confirmation, a sign-in that has gone, the switch and where focus lands, in light and dark at phone, tablet, desktop and embedded sizes.
• Add an image smoke check that the Codex sign-in reaches T3 Code when asked.

Changes: #84. Reported in #82.

Full changelog: v0.25.9...v0.25.10