fix(gui): open the selected file in the header open-in-app actions - #62056

Issue for this PR

Closes #61678, #62040

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

The header's "Open in app" button and the menu's "Copy path" always targeted the workspace root, so they opened and copied the folder instead of the file being viewed. The Windows and Linux Sublime Text entries named the app's display name, which the host can never resolve as a PATH command: the entry opened the file's default app on Windows and rejected on Linux.

• The header button and its menu target the pane's selected file tab, resolved to an absolute path, and fall back to the worktree folder while no file tab is open.
• Picking the file manager with a file tab selected now reveals the file in its folder instead of opening it in the default app; the worktree target still opens the folder.
• The Windows and Linux Sublime Text entries call the launcher's command subl, like their other entries; macOS keeps the display name, which is the correct form there.

No feature flag: behavior fix on an existing surface.

How did you verify your code works?

• Added a e2e regression in packages/app/e2e/regression/session-header.spec.ts for the panel open-in-app control: with no file tab open, "Copy path" yields the worktree path and the file manager opens the worktree folder; with a file tab open, the file manager records the file as revealed (not opened), "Copy path" yields the full file path, and the selected app (VS Code) opens the file; closing the tab restores the worktree target. This case fails on the pre-change behavior (worktree target and no reveal recording).
• bun run typecheck and bun test in packages/gui-plugins are green (1086 tests), including the open-in-app launch/check machine tests.
• bun run lint:changed at the repo root is green for the changed files.
• Verified the header's Open in actions manually in the Windows desktop app while a file tab was selected; the reveal path is the same code on all three platforms and is asserted through the revealed output in the e2e fixture.

Screenshots / recordings

Visual

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Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

Added by the opencode bot (AI-generated).

Fixes #62040
Fixes #55858