feat(agent): temporal video dedup — drop near-duplicate frames before the GPU

Near-static videos are the dominant GPU load: sampled into up to 64 frames, each
re-runs the whole detect→CCIP→SigLIP chain on ~identical content. Add a CPU
perceptual-hash frame dedup upstream of the GPU so the redundant frames are never
processed at all (not just their embeds).

- media.dedupe_frames() + _dhash(): 8×8 difference-hash (64-bit) per frame; greedy
  keep — a frame survives only if its hash differs from every kept frame by
  >= min_distance bits (Hamming). A static run collapses to one frame; genuinely
  distinct scenes all survive. Order + frame_time preserved.
- Called in worker._download_decode right after sample_frames, so it runs in the
  decode stage on the downloader thread (CPU) — the GPU consumers only ever see
  deduped frames, and buffered video items shrink (less RAM too).
- Env-tunable FRAME_DEDUPE_DISTANCE (default 8; higher keeps more frames for brief
  localized changes an 8×8 hash can miss; 0 disables). Logs `video frames N→M`
  when it drops any, so video load reduction is visible.

Complements the spatial per-frame crop dedup (2026-07-01.2); this is the temporal
axis. Build marker 2026-07-01.3.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ttrj5P7upUTueSfoJcxEqa

agent/fc_agent/config.py

@@ -38,6 +38,9 @@ class Config:
     max_regions: int      # hard cap on total regions per JOB (submit-size backstop)
     dedupe_iou: float     # crops overlapping >= this (same kind) are near-dupes,
     #                       dropped before the embed; >=1.0 disables it
+    frame_dedupe_distance: int  # video frames whose dHash differs by < this many
+    #                             bits are near-duplicates, dropped before detect;
+    #                             higher keeps more frames, 0 disables
 
     @classmethod
     def from_env(cls) -> Config:
@@ -65,4 +68,5 @@ class Config:
             max_figures=int(os.environ.get("MAX_FIGURES", "8")),
             max_regions=int(os.environ.get("MAX_REGIONS", "128")),
             dedupe_iou=float(os.environ.get("DEDUPE_IOU", "0.85")),
+            frame_dedupe_distance=int(os.environ.get("FRAME_DEDUPE_DISTANCE", "8")),
         )