• The folder input no longer remembers every file forever. data/folder_ingest.json
  keeps one fingerprint per processed file so a restart does not re-read the whole folder,
  but nothing ever pruned it — and the whole file is rewritten on every recording, so the
  per-file cost grew with everything before it. Measured: 453 bytes per entry, 160 ms per
  save at 50,000 entries, 660 ms at 200,000. At a thousand recordings a day that is over a
  second of pure bookkeeping per file after a year. Reported on the HA forum.
• New folder.max_indexed_files, default 5000, 0 disables the cap. Oldest entries go
  first; a file still being processed is never evicted. Dropping an entry costs nothing
  beyond reading that file once more if it is still there.
• Settable at runtime as Remember at most in the settings tab, which shows how many
  files are currently indexed against the limit.
• Enrolled faces are not affected. The gallery lives in data/persons and never
  expires — this cap only bounds the "already seen this file" notebook.
• Eviction happens once when a scan finishes, never in the middle of one: trimming between
  files would throw away entries the same scan had just written and re-process them.
  A folder that permanently holds more files than the cap now logs a warning, since every
  scan re-reads whatever fell out.
• Entries left in processing by a crash or a restart are reset for retry when the index
  is loaded. They are exempt from eviction, so without that they would accumulate until the
  cap could never be met again.
• The settings tab applies the limit through a locked, non-blocking path — it runs on the
  HTTP thread while the folder worker may be writing the same state.
• Documented that the folder input reads still images (.jpg, .jpeg, .png, .webp),
  not just video. It always could; the default extensions list is video-only and nothing
  said so, so a folder of images was skipped in silence.