Add a vision-model screenshot judge to the QA tooling

`tools/screen_designs.py judge` sends each capture together with its concept
mockup to a vision model and asks whether the capture realises the same screen and
layout intent. This covers what pixel/perceptual metrics cannot judge.

- Prompt explicitly ignores art style, fidelity, fonts, and placeholder text, since
  the references are stylised mockups.
- Verdicts are classed match / review (mismatch below --fail-confidence, default
  0.6) / diff (confident mismatch, exits non-zero) / unknown; --json, --only,
  --dry-run, --model supported.
- Reads the repo .env for OPENROUTER_API_KEY without overriding real env vars.
- Default judge model google/gemini-2.5-flash-lite; openai/gpt-4o-mini verified too.

Tests/docs
- 7 new offline tests in tools/test_screen_designs.py (request payload embeds both
  images, JSON/fenced/parts/non-JSON parsing, threshold classification, .env
  loading); 30 Python tests pass.
- Live run: 3 captures match, 3 review, 0 confident diffs.
- README, TODO section moved to DONE, MEMORY. Version 0.2.15.

README.md

@@ -31,7 +31,7 @@ The central design goal is simple:
 > Downloads are public (no sign-in required) since the host's instance-wide
 > `REQUIRE_SIGNIN_VIEW` was disabled on 2026-10-31.
 >
-> **Latest: v0.2.14** — string-formatting safety, plus public downloads (no sign-in) on the host.
+> **Latest: v0.2.15** — vision-model screenshot judge for the QA tooling.
 > Releases are built automatically when a `vX.Y.Z` tag is pushed
 > (see [`docs/RELEASING.md`](docs/RELEASING.md)); manual builds use
 > `./tools/build_releases.sh`. Installer/AppImage packaging runs in the same pipeline
@@ -205,13 +205,26 @@ python3 tools/screen_designs.py generate
 # Compare docs/screenshots/*.png against the designs
 python3 tools/screen_designs.py compare
 python3 tools/screen_designs.py compare --json
+
+# Ask a vision model whether each capture realises its design's screen and layout
+# (requires OPENROUTER_API_KEY; the repo .env is read automatically)
+python3 tools/screen_designs.py judge
+python3 tools/screen_designs.py judge --model openai/gpt-4o-mini --json
+python3 tools/screen_designs.py judge --only 03-   # one capture
+python3 tools/screen_designs.py judge --dry-run    # build requests, no network
 ```
 
 `compare` flags gross drift: wrong aspect ratio, undersized frame, near-blank
 frame, and large layout/palette/detail distance. It is a regression gate, not a
 semantic judge — pixel and perceptual metrics cannot decide whether a frame's
-composition is *right*, so a vision-model pass is the documented follow-up (see
-`TODO.md`). Regenerate the designs after changing screen layout, then re-run
+composition is *right*.
+
+`judge` covers that gap: it sends each capture together with its concept mockup to
+a vision model and asks whether the capture realises the same screen and layout
+intent. Art style, fidelity, fonts, and placeholder text are explicitly ignored.
+Verdicts are classed as `match`, `review` (a mismatch below `--fail-confidence`,
+default 0.6 — expected when a concept mockup is more stylised than the game), or
+`diff` (a confident mismatch, which exits non-zero). Regenerate the designs after changing screen layout, then re-run
 `compare` after regenerating the game screenshots with
 `src/test/capture_screenshots.gd`.