feat(perf): ship ModernFix dynamic_resources, add Flerovium and Iris Flywheel Compat

Bench (proxy 9900X/7800XT, see analysis/client-perf/RESULTS-proxy.md):
- ModernFix mixin.perf.dynamic_resources=true: startup -7.6 s, S1 p99
  9.11 -> 8.48 ms, S2 1% low 236 -> 264 fps (B6). Enforced packwiz file
  because ModernFix reads it before Default Options. Missing-texture check
  waived by owner; issues to be reported from play.
- Flerovium 1.1.2 (client): mob-pen S3 p99 ~0.9 ms better (B12b).
- Iris Flywheel Compat 2.4.0 (client): with a shaderpack, Create floor
  p99 13.3 -> 4.0 ms (Flywheel instancing kept under Iris) (B12b).
Deck tier already ships DH's LOW quality preset, so no DH change.

analysis/client-perf/proposed-configs/build.py

@@ -29,10 +29,10 @@ REPO = HERE.parents[2]
 # What `--ship` copies from out/T-default into the repo, and where.
 # Default Options seeds these client-side only, and only if the file is absent
 # (see README §1). Not shipped: sable-client.toml and sodium-options.json (no change
-# from upstream). modernfix-mixins.properties is held back until bench block B6
-# passes; when it does, add it here with destination "config/modernfix-mixins.properties"
-# (enforced packwiz file, because ModernFix reads it before Default Options runs) and
-# re-include it in .packwizignore.
+# from upstream). modernfix-mixins.properties ships as an *enforced* packwiz file
+# (ModernFix reads it before Default Options runs): bench B6 (proxy) showed
+# dynamic_resources -7.6 s startup and better S1/S2 frametimes; owner waived the
+# missing-texture check (2026-10-18) - report issues from play.
 DO = "config/defaultoptions"
 SHIP = {
     "options.txt": f"{DO}/options.txt",
@@ -45,6 +45,7 @@ SHIP = {
         f"{DO}/extra/config/sound_physics_remastered/soundphysics.properties",
     "config/sound_physics_remastered/sound_rates.properties":
         f"{DO}/extra/config/sound_physics_remastered/sound_rates.properties",
+    "config/modernfix-mixins.properties": "config/modernfix-mixins.properties",
 }
 
 # game-dir path -> (base file, format, may_append_new_keys)