docs: montage-renderer imagery, visual polish, README screenshots

- switch report frames to the scene best/worst montage renderer
  (Onscreen/Offscreen panels + TPI/FPI/FN legend): perfect-second hero,
  wedding couple, funeral 19-of-20, polygraph bridging, crew-scene FN
  ceiling, Robert Patrick ground-truth gap, rapid-cut double label,
  Herbie Hancock on an in-fiction screen
- deep dive restructured: extinction bridging framed as designed
  behavior with a measurable cost (debug overlay draws the boxes; the
  shipped output is presence windows), plus the face-vs-presence
  ceiling and two X-Ray-is-wrong exhibits
- Material polish: light/dark palette toggle, landing-page grid cards,
  figure/caption CSS, how-to-read admonition; site_url set so 404 links
  resolve under the Pages subpath
- README: perfect-second and screen-call frames committed (gitignore
  exceptions), readme_example.jpg retired
- build_site.sh: stage_frame helper downscales montage frames to 1920px
  and pulls any missing montage-frames packages

docs/index.md

@@ -5,32 +5,60 @@ film or TV episode — built on [KPN++](https://gitea.tourolle.paris/dtourolle/K
 (a C++20 Kahn Process Network library) for the detect → track → match → scene
 pipeline, with a Jellyfin-integrated gallery and an X-Ray-validated optimizer.
 
-This is what a good second looks like — one sampled frame from a held-out film,
-19 faces named, all 19 correct, the rest honestly declared unknown:
+This is a perfect X-Ray second, on a film the optimizer never saw:
 
-![19 correct identifications in one wedding shot, Downton Abbey: A New Era](assets/images/downton_wedding_19_correct.jpg)
+![A perfect X-Ray second: three faces named at 100%, two more correctly carried off-screen](assets/images/lovelace_perfect_second.jpg)
 
-And this is why the work isn't done: on this same film the same config misses
-6 in 10 of the actor-seconds X-Ray says are present, and on the worst held-out
-film it reports ghost actors over empty walls — at 100% confidence. Both
-stories, with the evidence, are in the pages below.
+Every visible face named at 100% — Chris Noth, Hank Azaria, Bobby Cannavale —
+the background extra honestly left unnamed, and the two credited cast without
+a visible face correctly carried as present off-screen by the tracker's
+presence windows. That's the pipeline exactly reproducing Amazon X-Ray's
+record for this second.
+
+It doesn't always go like that: the hardest held-out film scores 46% F1, and
+the report is honest about *why* — one tunable trade (extinction bridging at
+hard cuts), one structural ceiling (X-Ray credits people whose faces never
+appear), and a few cases where the pipeline is right and X-Ray is wrong. The
+evidence for all of it is in the pages below.
 
 ## Start here — four questions this bake-off answers
 
-- **[Which model is best?](best-model.md)** — calibration curves first
-  (discriminative power, independent of any threshold), then F1 on the actual
-  benchmark. LVFace-B Glint360K wins both.
-- **[Whole gallery vs. limited (cast-restricted) gallery](gallery-scope.md)** —
-  restricting the matcher to a film's credited cast is a clean win on every
-  axis (+3.3pp F1, less than a third the misIDs), but isn't a shipped runtime
-  feature yet.
-- **[Does pose expansion help?](pose-expansion.md)** — a real training-set
-  effect that didn't reproduce on 5 held-out films once two methodology bugs
-  were caught and fixed. An honest null result, not a forced narrative.
-- **[Deep dive: LVFace-B Glint360K](lvface-deep-dive.md)** — the winning
-  model's held-out generalization gap, its two real failure modes (frozen-bbox
-  "ghost tracks"), and one case where it correctly identified an actor that
-  the X-Ray ground truth itself failed to credit.
+<div class="grid cards" markdown>
+
+-   :material-trophy:{ .lg .middle } **[Which model is best?](best-model.md)**
+
+    ---
+
+    Calibration curves first (discriminative power, independent of any
+    threshold), then F1 on the actual benchmark. LVFace-B Glint360K wins
+    both.
+
+-   :material-filter:{ .lg .middle } **[Whole vs. cast-restricted gallery](gallery-scope.md)**
+
+    ---
+
+    Restricting the matcher to a film's credited cast is a clean win on
+    every axis (+3.3pp F1, less than a third the misIDs) — but isn't a
+    shipped runtime feature yet.
+
+-   :material-account-convert:{ .lg .middle } **[Does pose expansion help?](pose-expansion.md)**
+
+    ---
+
+    A convincing training-set effect that didn't reproduce on 5 held-out
+    films once two methodology bugs were caught and fixed. An honest null
+    result, not a forced narrative.
+
+-   :material-magnify-expand:{ .lg .middle } **[Deep dive: LVFace-B Glint360K](lvface-deep-dive.md)**
+
+    ---
+
+    The held-out generalization gap, how the error budget decomposes
+    (extinction bridging at hard cuts, X-Ray's scene-membership vs.
+    on-screen-face ceiling), and the frames where the pipeline is right
+    and the ground truth is wrong.
+
+</div>
 
 ## The full technical log
 
@@ -43,7 +71,7 @@ stories, with the evidence, are in the pages below.
   earlier scene-union-metric tuning pass, superseded by the per-second metric
   used in the bake-off but kept for the ground-truth/architecture background.
 - **[Service conversion (proposal)](service-conversion.md)** — design sketch
-  for an idle-GPU Docker worker, not yet built.
+  for a native idle-GPU worker gated on screen lock, not yet built.
 
 ## Reproducing the benchmarks