Phase 1: chunk store, tile rendering pipeline, and Leaflet viewer

api: WS gateway with token auth (Postgres-backed servers table, seeded via
`bun run seed`), column-granularity chunk store (hand-written SQL
migrations, no drizzle-kit CLI — its config loader needs esbuild, which
doesn't install cleanly here), dirty-chunk Redis stream producer with
per-flush dedup, and a tile-serving route.

worker: consumes the dirty-chunk stream via a proper consumer group,
rasterizes each chunk's columns into a single-resolution top-down PNG
(static pre-Flattening block-id palette), uploads to MinIO, and upserts
the tile pointer.

frontend: barebones Leaflet 2D viewer (CRS.Simple, one native zoom level)
wired to /api/servers and /api/tiles.

Object storage: tiles live in a dedicated `mcmapper-tiles` bucket on the
existing shared MinIO instance (devstack-minio on octo-winsrv) instead of
a per-stack container, via a scoped access key limited to that one bucket
— see README's "Object storage" section. MINIO_SECRET_KEY is real and is
deliberately not committed; docker-compose layers an untracked .env over
.env.example for it.

Full pipeline verified end-to-end against live containers: WS auth ->
Postgres upsert -> deduped Redis dirty-chunk event -> worker rasterize ->
MinIO upload -> tile fetch through the api route, including from the
actual mod-side WS client (see MCMapper-Mod's matching commit).

worker/src/render/mod.rs

@@ -2,6 +2,14 @@ mod cpu;
 
 pub use cpu::CpuRenderBackend;
 
+/// One rendered column within a chunk, in chunk-local coordinates (0..16).
+pub struct ColumnPixel {
+    pub local_x: u8,
+    pub local_z: u8,
+    pub block_id: u16,
+    pub block_meta: u8,
+}
+
 /// Swappable rendering strategy (CPU via rayon / GPU via wgpu / hybrid) selected at startup
 /// via the `RENDER_BACKEND` env var. Only the CPU path exists so far; GPU/hybrid land in
 /// Phase 8, with automatic fallback to CPU if `gpu`/`hybrid` is requested but no compatible
@@ -9,6 +17,7 @@ pub use cpu::CpuRenderBackend;
 pub trait RenderBackend: Send + Sync {
     fn name(&self) -> &'static str;
 
-    // Tile rasterization and chunk meshing methods land alongside their Phase 1/2 callers —
-    // no point defining signatures for data shapes that don't exist yet.
+    /// Rasterize one chunk's worth of columns (up to 256, sparse if the chunk isn't fully
+    /// synced yet) into a single-resolution top-down PNG tile, returned as encoded bytes.
+    fn rasterize_tile(&self, columns: &[ColumnPixel]) -> anyhow::Result<Vec<u8>>;
 }