feat: move items to XDG trash with D key (#12)

[phaethix]

Summary

• Adds interactive D to move selected/marked items into FreeDesktop XDG trash ($XDG_DATA_HOME/Trash, else ~/.local/share/Trash), keeping d = permanent delete and e = empty.
• Introduces DeleteAction through the TUI delete pipeline and implements remove.MoveItemToTrash with exclusive .trashinfo reservation, cross-device copy fallback, symlink/FIFO-safe handling, and no-clobber rename.
• Windows builds get a clear unsupported stub; help/--no-delete/archive guards match existing delete behavior.

Closes #12

Test plan

• go test ./pkg/remove/ ./tui/
• Cross-compile GOOS=windows / GOOS=linux for pkg/remove
• Manual: run gdu, press D on a file, confirm it appears under $XDG_DATA_HOME/Trash/{files,info}
• Manual: name conflict when Trash/files/<name> already exists → lands as <name>.2 without overwriting
• Manual: ? help shows D; with --no-delete, trash is disabled like delete/empty

Made with Cursor

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.38%. Comparing base (fe605ec) to head (1ecc49b).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #608      +/-   ##
==========================================
+ Coverage   85.89%   86.38%   +0.49%     
==========================================
  Files          55       59       +4     
  Lines        6329     6487     +158     
==========================================
+ Hits         5436     5604     +168     
+ Misses        689      681       -8     
+ Partials      204      202       -2     

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