Keep plant/temp control inert until a Sud is actually loaded

server/brewpi.py no longer pre-configures the real Pot's or Smith's model's
plant params at startup - there's no longer any generic baseline at all,
since the only source of truth is now a loaded Sud's own doc (applied via
tasks/sud.py's SudTask.apply_plant_params(), on Load and on every step).
Ambient temperature and PID gains stay configured at startup, since
they're independent of any Sud (global setting / hardware tuning, not
doc-derived).

Add Pot.is_configured() (already existed)/TempControllerBase.is_configured()/
TempController(Smith).is_configured(), and have tasks/pot.py's PotTask and
tasks/tempctrl.py's TcTask skip process() while not yet configured instead
of letting it raise - so plant and temp control are genuinely inert (not
crashing) until a Sud is loaded. "Normal" has no plant-model dependency,
so it stays active regardless.

Also refreshes README.md: removes stale tracer.py/.mat references (already
removed in an earlier commit), documents SudLogTask's JSON logs, the doc's
L/Td fields, and this inert-until-loaded behavior.

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

tasks/tempctrl.py

@@ -71,6 +71,12 @@ class TcTask(ATask):
 		await self.send({'Enabled': self.tc.enabled})
 
 		while True:
-			self.tc.process()
+			# Stays inert until set_params() (and, for a model-based
+			# controller like Smith, its model's plant params/ambient too
+			# - see components/pid/temp_controller_smith.py's
+			# is_configured()) has actually been supplied - process()
+			# would otherwise raise.
+			if self.tc.is_configured():
+				self.tc.process()
 			await asyncio.sleep(self.interval)