feat(app): add context menu to copy file paths in file tree

[cpkt9762]

Add right-click context menu to file nodes in the sidebar file tree with options to:

• Copy Relative Path
• Copy Absolute Path

Fixes #11820
Fixes #11620

Includes i18n translations for all 16 supported languages.

[github-actions]

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Related PR Found:

• PR feat(app): mention file via context menu in file tree #12448: "feat(app): mention file via context menu in file tree"
  • feat(app): mention file via context menu in file tree #12448
  • Why it's related: This PR also adds context menu functionality to the file tree. While it's focused on "mention file" functionality rather than "copy path", both PRs modify the file tree with right-click context menu features. There may be overlapping code changes or related functionality that should be reviewed for consistency.

[cpkt9762]

Thanks for linking #12448. This PR is complementary, not a duplicate:

• feat(app): mention file via context menu in file tree #12448 adds "Mention in prompt" functionality
• This PR adds "Copy Relative Path" and "Copy Absolute Path" for clipboard

Both features enhance the file tree context menu in different ways. If #12448 merges first, I can rebase to ensure clean integration.