Check off theta_amb backlog item now that it's config-driven

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

components/plant/TODO.md

@@ -27,11 +27,16 @@ the current `delay`-line rewrite of `Pot`.
   that nothing reads anymore — harmless but worth deleting (see
   `components/pid/TODO.md`'s config-validation item).
 
-- [ ] **`theta_amb` is hardcoded, not configured.** Still true —
-  `brewpi.py`: `pot = Pot(DT, pot_params, 20)` passes a literal `20`
-  instead of reading it from config or a live ambient sensor. Real
-  ambient temperature drifts and is never modeled as a disturbance, so
-  the controller's robustness to it is untested.
+- [x] **`theta_amb` is hardcoded, not configured.** Fixed: added a
+  top-level `ambient_temperature` key to `config.json`(`.templ`/`.sim`);
+  `brewpi.py` reads it once and passes it to both the real `Pot` and
+  (via a new `theta_amb` param) `temp_controller_smith.py`'s internal
+  models, so the Smith predictor's model matches the real plant's
+  assumed ambient instead of silently defaulting to 20. Real ambient
+  temperature still isn't modeled as a *drifting* disturbance (it's a
+  static config value, not a live sensor reading), so robustness to
+  ambient drift remains untested — that part of the original concern
+  stands.
 
 - [ ] **No actuator/process realism.** Partially improved: `process()`
   now clamps `self.temp` to `min(100, ...)` (won't simulate past