add: add editor bookmarks with gutter decorations

[ozgen]

Add per-repository bookmarks with slots 1-9.

Support setting bookmarks from the editor, changelist context menu, and Explorer context menu. Add jump and clear commands, overwrite confirmation, and clear-all support.

Render bookmark gutter decorations with numbered icons and line highlights. Persist bookmarks in workspace state and refresh decorations immediately after bookmark changes.

Also fix stale worklist file decorations after bulk Git operations by keeping stage-state refresh in sync with the decoration provider.

Update README, MANUAL, demo assets, and changelog for the new bookmark workflow.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 96.55172% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.63%. Comparing base (9ea334b) to head (2f14fca).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/views/bookmark/bookmarkDecorationProvider.ts	90.56%	3 Missing and 2 partials ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##             main      #34      +/-   ##
==========================================
+ Coverage   92.20%   92.63%   +0.43%     
==========================================
  Files          38       44       +6     
  Lines        1257     1399     +142     
  Branches      299      320      +21     
==========================================
+ Hits         1159     1296     +137     
- Misses         25       28       +3     
- Partials       73       75       +2     

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