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/plant/TODO.md

@@ -46,9 +46,10 @@ the current `delay`-line rewrite of `Pot`.
   and partially regressed: `Pot` also dropped its `gain` (heater
   efficiency) factor entirely — `process()` now applies 100% of
   commanded power with no loss, whereas before `params['gain']` could
-  model e.g. an 80% efficient transfer. `Model.gain`/`Plant.gain` are
-  now dead keys in `config.json.sim` (already absent from `.templ`) —
-  see `components/pid/TODO.md`'s config-validation item. Still no
+  model e.g. an 80% efficient transfer. `Model.gain`/`Plant.gain` were
+  dead keys in `config.json.sim` (already absent from `.templ`) before
+  that file was removed entirely — see `components/pid/TODO.md`'s
+  config-validation item. Still no
   heater power saturation enforced inside `Pot` itself (handled ad hoc
   in demo harnesses), no evaporation/lid heat loss, and no varying
   thermal mass `M` as volume changes (e.g. boil-off, adding