Phase 11: real block textures for 2D tiles

Layers texture-averaged colors on top of palette.rs's hand-picked table as a
fallback (color_for_textured), not a hard replacement — biome-tinted/animated
blocks (grass top, leaves, water, lava) deliberately keep the hand-picked
color since averaging their raw jar textures would be wrong, not just
imprecise.

Vanilla: worker/src/textures.rs downloads Mojang's official client jar
directly from launchermeta/piston-meta/piston-data (same endpoints the real
launcher uses, gated behind ACCEPT_MINECRAFT_EULA=true, off by default,
mirrors BlueMap's accept-download) and averages every block texture, cached
to disk so it's not re-downloaded every restart.

Modded: ingests block_registry/block_textures messages from the mod (new
Postgres tables + MinIO storage in api/src/textures.ts) — sent once per
connection over the existing WS gateway.

texturepacks/<name>/ (Dynmap-style flat PNGs) lets an operator override the
vanilla defaults worker-wide via TEXTURE_PACK. A per-server texturePack
admin column/API exists for the same purpose, but render-time per-server
resolution (of both the admin selection and the ingested modded textures) is
explicitly deferred — the worker still applies one process-wide palette; true
per-server resolution needs the render pipeline to thread a server-scoped
palette through the batch/GPU-dispatch path, judged too big a change for this
phase. Documented in README.

Docker was unavailable in this dev environment for the usual integration-test
verification; bunx tsc --noEmit was used as a fallback static check instead
(clean except 2 pre-existing unrelated errors in markers.test.ts).

worker/.env.example

@@ -28,3 +28,23 @@ RENDER_THREADS=auto
 # fewer, larger batches, less scheduling overhead per chunk on fewer/faster cores. Unrecognized
 # values fall back to `server`, matching this project's own primary deployment target.
 RENDER_PROFILE=server
+
+# Phase 11: set to exactly "true" to opt in to the worker downloading Mojang's official client
+# jar (from launchermeta/piston-meta/piston-data — the same endpoints the real launcher uses, so
+# this never redistributes anything, only fetches directly from Mojang) and averaging its block
+# textures into real colors, replacing palette.rs's hand-picked table. Mirrors BlueMap's
+# `accept-download` flag — off by default, since it's a real (if small, one-time, cached)
+# network fetch an operator should consent to.
+ACCEPT_MINECRAFT_EULA=false
+# Which Minecraft version's client jar to pull textures from — 1.12.2 (this project's primary
+# target) by default. Textures are looked up by file stem (e.g. "stone", "oak_planks"), which is
+# stable across the 1.7.10/1.12.2 era this project prioritizes.
+MC_TEXTURE_VERSION=1.12.2
+# Where the downloaded-and-averaged vanilla palette is cached (as JSON) so it isn't rebuilt on
+# every restart.
+TEXTURE_CACHE_DIR=./cache
+# Optional: name of a `texturepacks/<name>/` directory (flat *.png files, file stem = texture
+# name) whose colors are layered on top of the downloaded vanilla defaults — the Dynmap-style
+# operator-override mechanism. Currently applies worker-wide (this env var), not yet resolved
+# per-server from the admin panel's `texturePack` field — see README's Phase 11 note.
+#TEXTURE_PACK=