feat: add iii-sensor worker

sensor/Cargo.toml

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+[workspace]
+
+[package]
+name = "iii-sensor"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[[bin]]
+name = "iii-sensor"
+path = "src/main.rs"
+
+[dependencies]
+iii-sdk = "0.11.0"
+tokio = { version = "1", features = ["rt-multi-thread", "macros", "sync", "signal", "process"] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+serde_yaml = "0.9"
+anyhow = "1"
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["fmt", "env-filter"] }
+clap = { version = "4", features = ["derive"] }
+chrono = { version = "0.4", features = ["serde"] }
+walkdir = "2"

sensor/README.md

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+# iii-sensor
+
+The code your AI writes today is the context it reads tomorrow. Every session silently degrades your architecture unless you measure it. iii-sensor scans your codebase, computes a quality score across 5 dimensions (complexity, coupling, cohesion, size, duplication), saves baselines before agent sessions, and flags when quality drops. It's the feedback sensor in the harness engineering loop.
+
+**Plug and play:** Build with `cargo build --release`, then run `./target/release/iii-sensor --url ws://your-engine:49134`. It registers 6 functions. Call `sensor::baseline` before a coding session, then `sensor::compare` after to see what changed. Wire `sensor::gate` into your CI to reject PRs that degrade quality below your threshold.
+
+## Functions
+
+| Function ID | Description |
+|---|---|
+| `sensor::scan` | Walk a directory and compute per-file code quality metrics |
+| `sensor::score` | Aggregate quality score (0-100) from scan results using weighted power mean |
+| `sensor::baseline` | Save a named baseline snapshot for later comparison |
+| `sensor::compare` | Compare a fresh scan against a saved baseline to detect degradation |
+| `sensor::gate` | CI quality gate returning pass/fail on score thresholds |
+| `sensor::history` | Retrieve historical scores and compute trend direction |
+
+## iii Primitives Used
+
+- **State** -- baselines, score history, latest scan results (keyed by path hash)
+- **HTTP** -- all functions exposed as REST endpoints
+
+## Prerequisites
+
+- Rust 1.75+
+- Running iii engine on `ws://127.0.0.1:49134`
+
+## Build
+
+```bash
+cargo build --release
+```
+
+## Usage
+
+```bash
+./target/release/iii-sensor --url ws://127.0.0.1:49134 --config ./config.yaml
+```
+
+```
+Options:
+  --config <PATH>    Path to config.yaml [default: ./config.yaml]
+  --url <URL>        WebSocket URL of the iii engine [default: ws://127.0.0.1:49134]
+  --manifest         Output module manifest as JSON and exit
+  -h, --help         Print help
+```
+
+## Configuration
+
+```yaml
+scan_extensions: ["rs", "ts", "py", "js", "go"]  # file extensions to include
+max_file_size_kb: 512                              # skip files larger than this
+score_weights:
+  complexity: 0.25
+  coupling: 0.25
+  cohesion: 0.20
+  size: 0.15
+  duplication: 0.15
+thresholds:
+  degradation_pct: 10.0    # dimension drop % that flags degradation
+  min_score: 60.0           # minimum passing score for quality gate
+```
+
+## Tests
+
+```bash
+cargo test
+```

sensor/build.rs

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+fn main() {
+    println!(
+        "cargo:rustc-env=TARGET={}",
+        std::env::var("TARGET").unwrap()
+    );
+}

sensor/config.yaml

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+scan_extensions: ["rs", "ts", "py", "js", "go"]
+max_file_size_kb: 512
+score_weights:
+  complexity: 0.25
+  coupling: 0.25
+  cohesion: 0.20
+  size: 0.15
+  duplication: 0.15
+thresholds:
+  degradation_pct: 10.0
+  min_score: 60.0