feat(web): Core Refactor Phase A — extract sampling and cache modules; add adaptive TTL + eviction heuristics, Redis PoC, and metrics wiring. Tests added for TTL, eviction, exports, splash-adaptive, card index, and service worker. Docs+roadmap updated.

code/tests/test_preview_eviction_basic.py

@@ -0,0 +1,23 @@
+import os
+from code.web.services.theme_preview import get_theme_preview, bust_preview_cache  # type: ignore
+from code.web.services import preview_cache as pc  # type: ignore
+
+
+def test_basic_low_score_eviction(monkeypatch):
+    """Populate cache past limit using distinct color filters to force eviction."""
+    os.environ['THEME_PREVIEW_CACHE_MAX'] = '5'
+    bust_preview_cache()
+    colors_seq = [None, 'W', 'U', 'B', 'R', 'G']  # 6 unique keys (slug, limit fixed, colors vary)
+    # Prime first key with an extra hit to increase protection
+    first_color = colors_seq[0]
+    get_theme_preview('Blink', limit=6, colors=first_color)
+    get_theme_preview('Blink', limit=6, colors=first_color)  # hit
+    # Insert remaining distinct keys
+    for c in colors_seq[1:]:
+        get_theme_preview('Blink', limit=6, colors=c)
+    # Cache limit 5, inserted 6 distinct -> eviction should have occurred
+    assert len(pc.PREVIEW_CACHE) <= 5
+    from code.web.services.preview_metrics import preview_metrics  # type: ignore
+    m = preview_metrics()
+    assert m['preview_cache_evictions'] >= 1, 'Expected at least one eviction'
+    assert m['preview_cache_evictions_by_reason'].get('low_score', 0) >= 1