fix(app): make the subagent bar say what it is and drop dead controls - #57922

The bar shown when you view a subagent now says which subagent it is and what it is doing.
It used to be two rows with the agent, provider and model laid out like the composer's pickers, which can't be changed in a subagent session. Nothing said it was a subagent or what its task was.

❌ Before

1. A faint "Running · 24m 35s" line, then a second row with agent, provider, model and variant.
2. The model and variant looked like pickers but did nothing.
3. The task wasn't shown anywhere.

✅ After

1. One 44px line: "General subagent" followed by its task, cut off with a tooltip that shows the full task and the model.
2. The state: a spinner or Done/Failed/Interrupted icon, the word, and the elapsed or final time. A change fades in; a finished run opens at rest. Under 24rem wide the word hides.
3. "Main session" with its Esc hint, unchanged.

- <row>Running · 24m</row><row>agent  provider / model  variant  [Main session]</row>
+ <row>Surveyor subagent  task title…   ● Running · 24m   [Main session]</row>
+ tooltip: full task + model

📊 Proof (before above, after below; fictional titles)

Running, light and dark, done, failed, interrupted:

Permission dock above, right-to-left, narrow window, long title with tooltip:

The updated component test (bar names the subagent and its task, shows no model, no composer) fails on dev.

👀 Read: subagent-bar.tsx. Dev had since swapped the model's / for a shared slash component; that row is gone here, so the PR's version of the file replaced it. The rest is routine.

_{Seen in real use · stills were taken before the rebase onto dev · the rebase only touched the model row this PR removes}