fix(chat-input): make the textarea scrollable and reset it after submit

[philmerrell]

Problem

The chat input got awkward once the message grew long: you couldn't scroll inside the textarea, the expansion felt clunky, and it stayed expanded after sending.

Three separate causes:

1. No scrolling — the textarea carried overflow-hidden, so once content exceeded the visible area there was no way to reach it.
2. Clunky expansion — onTextareaInput set height = scrollHeight with no clamp. Past 200px the inline height kept growing while max-height: 200px capped the rendered height, leaving the element's real and displayed heights diverged and the scrollbar unreachable.
3. No reset after submit — submitChatRequest cleared the value but left the stale inline height behind.

Changes

• overflow-hidden → overflow-y-auto on the textarea.
• Growth clamped to the max in a shared autoResize().
• New resetTextareaHeight() called on submit.
• Removes the .chat-textarea CSS block — it declared its own min-height/max-height/field-sizing: content, but the class is applied nowhere in the template, so the rules were dead while contradicting the real inline styles. The JS path is now the sole sizing authority, with the inline min-height/max-height as the CSS backstop.
• Removes the isExpanded signal — written on submit, never read.

Verification

Verified live against the dev backend on localhost:4200:

Check	Result
Grow → clamp at max	inline height 200px, content 992px — no longer overruns
Scroll inside textarea	overflow-y: auto, scrollTop moves 0 → 792
Reset after submit	inline height 152px → 60px, scrollTop 0
Shrink while deleting	200 → 104 → 60

npx tsc --noEmit clean.

⚠️ Worth knowing for anyone re-testing: the first submit from the home screen creates a session and remounts the component, so the input collapses whether or not the fix works. The reset was confirmed on a second, in-session submit where the component instance is reused (inline height lands on an explicit 60px rather than empty string).

🤖 Generated with Claude Code