fix(capture): scope the own-staging guard to the image file-flavor only

[davidboulay]

Symptom

Recovering a file from history played no copy sound and never synced to the paired device.

Cause

Two unrelated things staged into DATA_DIR/paste:

Writer	What	Should capture see it?
storage.paste_path()	a recovered file, copied out under its original name so the paste isn't named after its sha256	yes — a genuine user clip
_stage_image()	throwaway backing file for an image also offered as a file; its uri-list bounces back through wl-paste --watch	no — pure echo

_is_own_staging matched the whole directory, so it dropped both:

file_paths = [p for p in clipboard.read_file_paths(types) if not _is_own_staging(p)]

With no file path surviving and no image/png on the clipboard, capture_current() fell through to new_id = None. _cmd_store (cli.py:77-85) then sent no _current, no refresh, no _broadcast, and never reached the sound.play() inside if new_id is not None.

The panel's storage.touch() still moved the entry to the front, so the recover looked like it worked. Measured: entry 8939 recovered at 22:10:13 while .last_sound still held 8946 from 22:10:00 — capture ran and stored nothing.

Fix

_stage_image writes to FLAVOR_DIR (paste/.image-flavor/); the guard matches only that. The echo it exists for is still suppressed; file recovers now capture normally, so the sound and the broadcast come back.

Both directories are named in config.py instead of being spelled out at three call sites — that duplication is what let them drift into one.

Re-capturing a recovered file is harmless: add_file_from_path dedupes on the content hash and returns the existing id (bumping created_at), so no duplicate entry.

Tests

scripts/capture_staging_test.py (new, wired into CI) pins the two apart — including the cross-module case that actually broke: whatever paste_path() hands the panel must survive capture's filter. Against the old guard:

FAIL: capture staging guard is wrong:
  recovered file must be captured, not ignored — this is the bug: no copy sound and no sync broadcast on a file recover
  paste_path output must not be treated as own staging — /tmp/…/paste/Report Q3.pdf

Full suite green locally: selector prototypes, mac pasteboard, capture staging, sync core, device-id drift, sync delivery.

Note

Existing files already staged in paste/ from before this change are unaffected — they're only ever overwritten per recover. Nothing migrates and nothing needs cleaning up.