feat: always write a fixed-name copy of server/sud logs, use .json for sud logs

Alongside the dated log files, ServerLogTask/SudLogTask now also write
(and overwrite) a fixed-name copy on every write() - logs/log_latest.json
and logs/log_latest_sud.json - so a dashboard/tail-style consumer can
point at one unchanging path instead of tracking the current run's
timestamped filename.

Also switches SudLogTask's own dated/latest filenames from .log to .json,
matching what they've always actually contained. This incidentally fixes
utils/analyze_log.py's two-argument CLI form, which already assumed a
.json extension for sud logs.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JFDeoTKBDkXRhPfnyDEoBt

tasks/sud_log.py

@@ -11,7 +11,7 @@ class SudLogTask(ServerLogTask):
 	"""Records temp/power samples for a single Sud run - same sample format
 	as ServerLogTask, but only while a run is active: recording starts on
 	Play and is written out on Stop (or natural completion), to
-	logs/log_{date_time}_{sud_name}.log. A Pause/resume doesn't start a new
+	logs/log_{date_time}_{sud_name}.json. A Pause/resume doesn't start a new
 	file - only a fresh Play (from IDLE/DONE) does."""
 
 	def __init__(self, tc: APid, heater: AHeater, heater_task, sud, interval, path='./logs', config=None, dt=None, log_interval=None, sim_warp_factor=None):
@@ -26,7 +26,14 @@ class SudLogTask(ServerLogTask):
 
 	def _filename(self):
 		name_part = _safe_filename_part(self.sud.name or 'Sud')
-		return 'log_{}_{}.log'.format(self._run_id, name_part)
+		return 'log_{}_{}.json'.format(self._run_id, name_part)
+
+	def _latest_filename(self):
+		# Fixed regardless of which schedule is running, unlike _filename()
+		# above - a dashboard/tail-style consumer can point at one
+		# unchanging path across different Suds, not just different runs
+		# of the same one.
+		return 'log_latest_sud.json'
 
 	def _log_name(self):
 		return self.sud.name