docs: archive the July 2026 report; new methodology for the opencv5 run

The July report (4-model ArcFace/LVFace bake-off, pre-opencv5 framework,
3-film training + held-out validation) is superseded by the opencv5 build:
single-model LVFace-B, a 6-knob DE sweep over all 9 films, flood-fill
presence, and the registry/decode fixes. Rather than overwrite it, archive
it date-suffixed and start the current report fresh.

- Rename the six July result pages to *-2026-07.md, rewrite their
  intra-archive cross-links, and add an "Archived (July 2026)" banner to each.
- mkdocs nav: current report at top, the July set under an Archive section.
- New docs/methodology.md for the opencv5 run: corrects the withdrawn
  anneal_sec/extinction_sec presence bridging (windows are now
  [first_seen, last_seen], AR-012/013), documents the two presence modes
  (track_extent / flood), and records that every eval scores all 9 films.

The current experiment log (model-bakeoff.md) and Home rewrite land once
the DE sweep converges and the final optimum is known.

mkdocs.yml

@@ -36,13 +36,15 @@ nav:
   - Home: index.md
   - How We Score Against X-Ray: methodology.md
   - Benchmark — SuperHero: benchmark.md
-  - Findings:
-    - Best Model: best-model.md
-    - Gallery Scope (Full vs. Limited): gallery-scope.md
-    - Pose Expansion: pose-expansion.md
-    - LVFace Deep Dive: lvface-deep-dive.md
   - Full Experiment Log: model-bakeoff.md
   - Service Conversion (proposal): service-conversion.md
+  - Archive (July 2026):
+    - How We Scored (July): methodology-2026-07.md
+    - Best Model: best-model-2026-07.md
+    - Gallery Scope (Full vs. Limited): gallery-scope-2026-07.md
+    - Pose Expansion: pose-expansion-2026-07.md
+    - LVFace Deep Dive: lvface-deep-dive-2026-07.md
+    - Full Experiment Log (July): model-bakeoff-2026-07.md
 
 markdown_extensions:
   - admonition