fix(landscape): guard redelivery, detach terminal writes, bound workers

F2: Execute had no status guard, so a redelivered or stale message reran a
finished run. Runs that are neither queued nor running are logged and acked
without work; "running" still executes so a worker that crashed mid-run
recovers.

F4: failRun, finishNodeFailed and MarkRunFailed wrote the terminal status on
the caller's context, which is exactly the context that is already cancelled
when the run failed because of a shutdown or a sibling node — the write was
refused and the run stayed stuck in "running". They now write on a
context.WithoutCancel copy with a 10s timeout; the consumer's best-effort
MarkRunFailed does the same.

F5: peak memory scaled with the host's core count. LP_MAX_WORKERS (default 8)
is now the total window-worker budget of a run and LP_MAX_NODES (default 2) the
node fan-out; each node gets max(1, workers/nodes) through the new
landscape.ComputeWithWorkers. Compute and service.ComputeFunc keep their
signatures: Compute delegates with MaxWorkersPerNode, and a legacy ComputeFunc
handed to NewLandscapeService is wrapped.

F6: the stage loop used a plain errgroup, so a failing node let its siblings
run to completion. It now uses errgroup.WithContext and passes the group
context into runNode, cancelling siblings mid-compute.

F7: wrap every float32 product in an explicit conversion so the compiler
cannot fuse it into an FMA, keeping the kernels bit-identical to numpy's
per-op rounding.

F8: README's builder package list now matches the Dockerfile (adds g++), and
the Landscape section documents the memory model and the two new knobs.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

.env.example

@@ -9,4 +9,8 @@ S3_SECRET_KEY: minioadmin
 S3_BUCKET: geofiles
 S3_USE_SSL: "false"
 
-DB_PORT=5423
+DB_PORT=5423
+
+# Landscape Program parallelism (bounds worker peak memory)
+LP_MAX_WORKERS=8
+LP_MAX_NODES=2