Reduce terminal drawer resize rerenders

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What Changed

• Reworked ThreadTerminalDrawer height handling so prop-driven height changes render from the clamped source height directly instead of syncing through setState in an effect.
• Kept transient drag/window-resize height updates local to a named useThreadDrawerHeight hook.
• Replaced the visibility-only resize effect with a derived resize epoch signal.
• Added React Scan recordings for the audited interaction:
  • Before: docs/perf/react-scan-terminal-drawer-before.webm
  • After: docs/perf/react-scan-terminal-drawer-after.webm

Why

React Doctor flagged ThreadTerminalDrawer for synchronous state updates in effects, which can create cascading renders and block React Compiler optimization. The new flow removes the prop-to-state effect from the component's hot resize path while preserving live drag behavior and terminal fit synchronization.

React Doctor summary improved from 606 diagnostics / 141 errors to 605 diagnostics / 139 errors, with the targeted ThreadTerminalDrawer set-state-in-effect findings removed.

UI Changes

No intentional UI appearance change. The before/after React Scan recordings above show the same terminal drawer height/visibility interaction with React Scan enabled.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

Validation:

• bun fmt
• bun lint (passes with existing warnings)
• bun typecheck
• bunx react-doctor@latest --json --yes --offline --fail-on none

  

Note

Reduce rerenders in ThreadTerminalDrawer during resize

• Introduces a useThreadDrawerHeight hook in ThreadTerminalDrawer.tsx that manages drawer height with a per-thread draft value, suppressing redundant onHeightChange calls when the clamped height hasn't changed.
• Replaces a resizeEpoch effect (triggered on visibility changes) with a derived effectiveResizeEpoch = resizeEpoch + (visible ? 1 : 0), reducing unnecessary re-renders of TerminalViewport children.
• Draft height is cleared after drag-end and non-drag window resize events, so only in-progress drag interactions use the draft value.
• Behavioral Change: TerminalViewport instances now always receive a resizeEpoch incremented by 1 when the drawer is visible, rather than incrementing only on visibility transitions.

^{Macroscope summarized c5320d7.}