* perf: implement virtualized rendering for diff viewer
- Enables efficient rendering of large diffs by only rendering visible content
- Uses shared virtualizer cache to optimize memory across multiple diff viewers
- Configures virtual scrolling with 24px line height for consistent layout
* fix: improve diff viewer line selection and annotation rendering
* fix: normalize line ranges to prevent selection bugs
* chore: upgrade @opencode-ai/sdk to v1.1.65