docs: client-perf analysis, bench harness and work journal

Everything the next agent needs to run the Phase 2 optimisation loop on a
machine that can launch the client:

- analysis/client-perf/: LEVERS (ranked levers + corrections), BENCH-MATRIX
  (world, scenes, config IDs, blocks B0-B14 with decision rules),
  PLAYER-TUNING, SPAWN-TUNING, research briefs, the jar scanner and its
  output, observed default configs, and proposed-configs/ (build.py
  generates tiers and bench variants and fails on unknown keys;
  apply_variant.py applies a variant and merges options.txt).
- analysis/client-perf/bench/onion-bench/: bench-world datapack (scene
  teleports, Create grid, mob pen, sound storm, 120 s teleport tour).
- analysis/audit/: the static recipe/dependency audit, including gen_fixes.py,
  which generates the shipped Paxi datapack and was never tracked.
- phase0/: per-machine measurement harness (Steam Deck, 7700K/1060,
  6700K/1080 Ti).
- .pi/journal.md: running work log; read it first.

All of it is packwizignored, so nothing here ships to players.

analysis/client-perf/data/observed-default-configs/skinlayers.json

@@ -0,0 +1,20 @@
+{
+  "enableHat": true,
+  "enableJacket": true,
+  "enableLeftSleeve": true,
+  "enableRightSleeve": true,
+  "enableLeftPants": true,
+  "enableRightPants": true,
+  "baseVoxelSize": 1.15,
+  "bodyVoxelWidthSize": 1.05,
+  "headVoxelSize": 1.18,
+  "renderDistanceLOD": 14,
+  "enableSkulls": true,
+  "enableSkullsItems": true,
+  "skullVoxelSize": 1.1,
+  "fastRender": true,
+  "compatibilityMode": true,
+  "irisCompatibilityMode": false,
+  "applySodiumWorkaround": false,
+  "firstPersonPixelScaling": 1.1
+}