Consolidate config.json.sim into config.json.templ

config.json.templ's component names already default to "sim" for every
backend (sensor/heater/stirrer/plant), making the separate .sim template
mostly redundant - it only differed in dt/sim_warp_factor/PID gain tuning,
which .templ now adopts directly. Removes config.json.sim, updates
brewpi.py's CLI args (-m/--logdir replaces the unused -d/--model/--sim
flags), and refreshes the README/TODO references that pointed at the now-
removed file.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DkkuG48uHFCGKe6dPSERFk

components/pid/TODO.md

@@ -58,10 +58,10 @@ git history for `temp_controller.py`/`temp_controller_smith.py`).
   schema/dataclass validation layer at config-load would surface
   errors immediately instead of mid-`__init__` — and would have caught
   the dead `TempCtrl.Kalman` / `Model.kn` / `Plant.kn` keys that used
-  to sit unused in `config.json.templ`/`.sim` (since deleted) and the
-  `Model.gain`/`Plant.gain` keys still doing the same in
-  `config.json.sim` right now — `Pot` dropped `gain` entirely, see
-  `components/plant/TODO.md`.
+  to sit unused in `config.json.templ`/`.sim` (since deleted), and the
+  `Model.gain`/`Plant.gain` keys that did the same in `config.json.sim`
+  before that file was removed entirely — `Pot` dropped `gain`
+  entirely, see `components/plant/TODO.md`.
 
 - [ ] **`kalman.py` is now dead code in production.** Neither
   `temp_controller.py` nor `temp_controller_smith.py` uses `Kalman`