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).

src/config.rs

@@ -6,13 +6,6 @@ pub struct Config {
     pub frame_stream: String,
     pub consumer_group: String,
     pub consumer_name: String,
-    pub stream_block_ms: usize,
-    pub stream_batch_size: usize,
-    pub database_url: String,
-    pub model_path: String,
-    pub model_input_size: u32,
-    pub confidence_threshold: f32,
-    pub intra_op_threads: usize,
 }
 
 impl Config {
@@ -22,21 +15,10 @@ impl Config {
             frame_stream: env_or("CONTINUUM_FRAME_STREAM", "stream:camera_frames"),
             consumer_group: env_or("CONTINUUM_CONSUMER_GROUP", "ai-worker"),
             consumer_name: env_or("CONTINUUM_CONSUMER_NAME", "ai-worker-1"),
-            stream_block_ms: env_or("CONTINUUM_STREAM_BLOCK_MS", "5000").parse()?,
-            stream_batch_size: env_or("CONTINUUM_STREAM_BATCH_SIZE", "16").parse()?,
-            database_url: require("DATABASE_URL")?,
-            model_path: env_or("CONTINUUM_MODEL_PATH", "./models/failure-detector.onnx"),
-            model_input_size: env_or("CONTINUUM_MODEL_INPUT_SIZE", "640").parse()?,
-            confidence_threshold: env_or("CONTINUUM_CONFIDENCE_THRESHOLD", "0.75").parse()?,
-            intra_op_threads: env_or("CONTINUUM_INTRA_OP_THREADS", "4").parse()?,
         })
     }
 }
 
-fn require(key: &str) -> anyhow::Result<String> {
-    env::var(key).map_err(|_| anyhow::anyhow!("missing required env var {key}"))
-}
-
 fn env_or(key: &str, default: &str) -> String {
     env::var(key).unwrap_or_else(|_| default.to_string())
 }