perf: Optimize rendering and clean up persist/UI code

[mhiro2]

Summary

• Improve rendering performance by caching treesitter captures and repo-root resolution per render cycle
• Optimize session restore by batching reflow operations to reduce UI flicker
• Unify all notification calls through util.notify for consistent message handling
• Drop unused scope options from persist module and clean up type definitions
• Fix session list command to display names in sorted order

Changes

• 030fa2e : perf(persist): batch session restore reflow
  • Batch stack reflow during session restore to prevent UI flicker
  • Add tests for batch restore behavior
• 6c74d11 : perf(stack-view): cache preview treesitter captures
  • Cache treesitter highlight captures per render to avoid redundant parsing
  • Refactor render.lua to support per-render cache lifecycle
• 3530be2 : perf(path): cache repo-root resolution per render
  • Cache repo-root path resolution within each render cycle
  • Add string utilities for path handling with tests
• 36dd935 : refactor(persist): drop unused scope options
  • Remove unused scope parameter from persist functions
  • Update documentation to reflect simplified API
• c173398 : refactor(notify): unify notifications via util notify
  • Centralize all notification calls through util.notify module
  • Enable consistent notification level handling across the codebase
• 7c0e714 : fix(commands): sort session names in list
  • Sort session names alphabetically in :PeekstackSessionList output
  • Add test coverage for sorted list behavior
• 682a06a : chore(types): align session item optional fields
  • Align optional field annotations in SessionItem type definition
  • Add tests to verify type field handling