feat(snapshot): re-encode captures + disk-pressure retention

Camera snapshots were stored RAW — the camera's full-res JPEG straight into
the BLOB, no resize/recompress. Measured on the dev DB: 300 snapshots = 81.7 MB
= ~72% of the 114 MB SQLite file (the big ones 2688×1520 / ~600 KB, Hikvision
main stream). They dominated the appliance's single backed-up DB file.

Re-encode on capture (snapshot.ts):
- Downscale each frame to SNAPSHOT_MAX_EDGE (1280px long edge) + recompress at
  SNAPSHOT_JPEG_QUALITY (80) via sharp (libvips, Apache-2.0) before storage —
  ~6-10× smaller (verified 2688×1520 → 1280×724, ~8×), plate still readable,
  clean image/jpeg (drops the camera's charset cruft). STORAGE-ONLY: recognition
  keeps the ORIGINAL full-res bytes (downscaling hurts OCR). Fail-soft — a
  re-encode error stores the original, never drops the snapshot or blocks the
  (already-open) path. sharp lives in apps/server (owns the capture path), where
  bcrypt already establishes the native-dep pattern.

Disk-pressure retention (snapshot-retention.ts) — a SAFETY VALVE, not the daily
mechanism (the re-encode does that). Daily check reads the DB filesystem used%
(statfs on db.$client.name); no-op unless ≥ SNAPSHOT_DISK_HIGH_PCT (70). Over the
mark: delete the OLDEST until an estimated SNAPSHOT_DISK_FREE_TARGET_PCT (10%) of
disk is freed — never below SNAPSHOT_MIN_KEEP (500) — then VACUUM once to return
space to the OS. A DELETE only frees SQLite pages (disk doesn't drop until VACUUM),
so the loop is driven by estimated freed bytes (SUM(length(bytes))), not a live
disk re-read; the prune owns the DB-locking VACUUM, run daily off-peak. diskUsage
is injectable for tests. None of this touches the signed ledger — snapshots are
unsigned/advisory, referenced only by id.

Tests: encodeForStorage (downscale / clean-type / no-enlarge / fail-soft) +
pruneSnapshots (no-op below mark / delete-oldest-to-target + VACUUM / MIN_KEEP
floor / skip-VACUUM-when-empty). All four snapshot env knobs documented in the
komodo env reference. Full workspace build/lint/test green; the prune smoke-verified
on a scratch DB copy (file shrank after VACUUM).

Existing ~81.7 MB of raw snapshots are unchanged (a one-off re-encode backfill is
a separate optional follow-up). Updated entry-exit-points + technology-stack wiki.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

komodo/.env.komodo.example

@@ -60,6 +60,14 @@ WS_ALLOWED_ORIGINS=
 # LOG_RETENTION_DAYS=30              # app_logs auto-purge age
 # LOG_RETENTION_MAX_ROWS=50000      # app_logs row cap
 # RECYCLE_BIN_RETENTION_DAYS=30      # soft-deleted items auto-purge age (0 = keep forever)
+# --- snapshots (camera evidence; stored re-encoded, then pruned under disk pressure) ---
+# SNAPSHOT_MAX_EDGE=1280             # downscale long edge (px) before storing
+# SNAPSHOT_JPEG_QUALITY=80           # stored JPEG quality (recognition uses full-res original)
+# Disk-pressure prune (daily safety valve; deletes oldest + VACUUM only when the disk is tight):
+# SNAPSHOT_DISK_HIGH_PCT=70          # prune only when the DB's filesystem is ≥ this % used
+# SNAPSHOT_DISK_FREE_TARGET_PCT=10   # try to free ~this % of the disk per run
+# SNAPSHOT_MIN_KEEP=500              # never prune below this many snapshots (floor)
+# SNAPSHOT_PRUNE_BATCH=200           # delete oldest in batches of this many
 # --- device monitor / lane ---
 # DEVICE_POLL_MS=8000                # device health poll interval
 # PRINTER_POLL_MS=5000               # printer status poll interval