feat(components): add Copy file path to the desktop file viewer

[pythonlearner1025]

MobileFileViewerDrawer has carried this action since it landed, under
sessions.fileViewer.copyPath, and ui/diff-viewer/diff-file-header-actions.tsx
draws the same button with the same key. The desktop viewer has no way to get at
the path it is showing.

Add the button to the viewer toolbar, before the search control. The path is
knowable for every file the viewer can show, binary previews included, so the
control has no condition of its own beyond a non-empty path, and it joins
showViewerTopBar so a file whose toolbar was otherwise empty still gets one.

Adds sessions.fileViewer.pathCopyFailed beside the existing pathCopied.

Compatibility

Every change is additive at its default. With the new prop, parameter or flag
absent, the touched components render and behave exactly as they do today, and
no existing call site in this repository passes one.

Testing

packages/components typecheck and the full vitest suite pass. No new test: the viewer needs a file provider to mount.

Notes for the reviewer

Adds sessions.fileViewer.pathCopyFailed to en.json and zh_CN.json, beside the existing pathCopied.

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Review metadata

BlitzOS fork only. Delete this section before sending the PR to LodyAI/Lody.

Branch	blitz/seam-10-copy-file-path
Branched from	f3474894 (the pinned upstream commit)
Classification	A — small missing feature, parity fix
Suggested submit priority	P3
Vendor seam patch	10 (SP28)

locales/en.json                                    |  1 +
 locales/zh_CN.json                                 |  1 +
 .../sessions/session-file-content-view.tsx         | 29 +++++++++++++++++++++-
 3 files changed, 30 insertions(+), 1 deletion(-)