fix(picker): Resolve picker paths in their own cwd and keep caller actions

[mhiro2]

Summary

• Grep and fzf-lua results are resolved against the directory the search ran in, not the editor cwd at confirm time
• fzf-lua actions and Telescope attach_mappings passed by the caller are kept; only the confirm action is replaced
• The stack view keeps highlights of unchanged lines after a partial redraw, and diagnostic popups underline multi-line ranges correctly

Changes

• 3963bb8 : fix(grep): resolve results in the directory the search started in
  • The cwd is pinned before the rg > prompt and used both to run rg and to resolve its relative paths, so :cd while the prompt or rg is pending no longer opens a same-named file in the other directory
  • Directory names containing $VAR are no longer expanded during resolution
• 54b99e0 : fix(fzf-lua): resolve entries against the picker cwd
  • The wrappers and actions.push parse the entry with the picker opts fzf-lua passes to the action, so a picker opened with its own cwd resolves relative files, grep matches and references correctly
  • actions.push(selected, opts, push_opts) now takes the picker opts and peekstack's provider/mode separately; mode is no longer forwarded to fzf-lua, and a missing line or column no longer becomes position -1
• ca02d56 : fix(extensions): keep the caller's picker actions and mappings
  • fzf-lua receives the caller's actions (table or function) with only the confirm action swapped, so custom actions such as ctrl-q keep working
  • Telescope maps <CR> and then runs the caller's attach_mappings, returning its result so callers can still override keys
• e7ad48d : fix(stack-view): keep highlights of unchanged lines on partial redraw
  • The replaced range is cleared before the lines are swapped, so entries and Tree-sitter preview colors that move up after a removal keep their highlights
  • The first render replaces the empty line of the new buffer instead of leaving it below the list
• 868c232 : fix(diagnostics): keep the end column of multi-line diagnostics
  • Start and end columns are only ordered within one line and each is clamped to its own line, so a range ending early on a later or short line keeps its underline
  • Ranges crossing the top or bottom of the popup buffer are clipped to the visible lines, and ranges fully outside are not underlined