Simplify boilerplate for learning: stub inference and Postgres write

Removed ort/ndarray/image (ONNX Runtime inference) and sqlx (Postgres audit
write). inference::detect() and the Postgres half of reporter::report() are
now stubs with a comment for what real code goes there. Redis Streams
XREADGROUP loop and the Redis pub/sub alert stay real.

Verified with a clean cargo check --all-targets (0 warnings).

.env.example

@@ -1,18 +1,6 @@
-# Redis Streams
 CONTINUUM_REDIS_URL=redis://localhost:6379
 CONTINUUM_FRAME_STREAM=stream:camera_frames
 CONTINUUM_CONSUMER_GROUP=ai-worker
 CONTINUUM_CONSUMER_NAME=ai-worker-1
-CONTINUUM_STREAM_BLOCK_MS=5000
-CONTINUUM_STREAM_BATCH_SIZE=16
-
-# Postgres (fast-path alert writes; same database as continuum-backend)
-DATABASE_URL=postgres://continuum:continuum@localhost:5432/continuum
-
-# Inference
-CONTINUUM_MODEL_PATH=./models/failure-detector.onnx
-CONTINUUM_MODEL_INPUT_SIZE=640
-CONTINUUM_CONFIDENCE_THRESHOLD=0.75
-CONTINUUM_INTRA_OP_THREADS=4
 
 RUST_LOG=info,continuum_ai_worker=debug