perf(ui): keep wrapped large diffs responsive

[mplibunao]

Fixes #600

Summary

• Enable exact file-level windowing for wrapped reviews instead of mounting every file section.
• Highlight selected and visible files immediately, while deferring speculative neighbor/offscreen highlighting until navigation is idle.
• Share wrapped-row width budgets between rendering and geometry, including note-guide and add-note columns.
• Give no-hunk messages an explicit two-row body so window spacers and mounted content stay aligned.
• Add component, geometry, render-window, and PTY regressions for wrapped navigation and rapid scrolling.

Why

Wrapping previously bypassed file-level windowing. On a large review this mounted the entire file stream and eagerly queued syntax highlighting on the main thread, producing a blank startup and high memory use. Exact precomputed section geometry now lets wrapped reviews mount only nearby files without changing scroll or hunk-navigation coordinates.

Validation

• bun run lint
• bun run format:check
• bun run typecheck
• bun run check:docs
• bun run changeset:status
• 96 focused unit/component tests
• 15 targeted PTY tests, including wrapped cross-window hunk navigation and rapid scroll-to-edge recovery
• 64/64 PTY integration tests with an isolated Git/TMP environment
• Compiled binary build
• Frozen 142-file wrapped review (20,853 insertions / 1,480 deletions, 216x60 Kitty), 5/5 valid runs:
  • first paint median 1.403s, max 1.505s
  • peak RSS max 348,618,752 bytes
  • prior affected baseline did not paint within 30s and reached 1,242,595,328 bytes
• Literal local wrapper launch with the compiled candidate: paint, hunk navigation, and clean quit all passed

The broader macOS bun run test attempt reached 1,474 passing and 17 skipped tests; three pre-existing session E2E cases remained host-dependent because the harness assumes Linux script behavior and has daemon timing sensitivity. The changed surface and PTY integration suites pass, and upstream Linux CI remains authoritative for those session cases.

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