Close the scan → catalog loop (LF scan path + cataloger handoff)

[fhwrdh]

The missing quarter of the shoot → dev → scan → catalog pipeline (north star: "anything that leaves a manual gap between stages is unfinished").

• LF (4×5) scan path — no working route today; Valoi rig is 35/120 only. Evaluate V850 flatbed vs. DSLR tile-stitch.
• Cataloger handoff — consistent naming ({dev_id}_{frame:02}.ext), per-frame XMP sidecars (film/ISO/dev/camera/lens/location), per-dev_session manifest export.
• Keep it cataloger-agnostic (LR today; darktable/digiKam/C1 later) — standard XMP + filesystem conventions.

Ref: ROADMAP.md §Scanning.