log: stamp mirrored stdout/stderr lines with <date>T<time>

Tee (server/brewpi.py) mirrors print() output to logs/brewpi.*.log but
previously wrote it verbatim, so those files had no timestamps to
correlate against the JSON sample logs. Prefix each line instead.

server/brewpi.py

@@ -25,14 +25,32 @@ class Tee:
 	"""Duplicates writes to multiple streams - used to mirror stdout/stderr
 	(everything the rest of the codebase already reaches via print()) into
 	a log file under logs/ as well as the console, without having to touch
-	every print() call site."""
+	every print() call site.
+
+	Also stamps every line with a "<date>T<time>:" prefix (existing print()
+	call sites already start their message with "Component: ..." - see e.g.
+	tasks/stirrer.py - so the combined line reads
+	"<date>T<time>:<component>: <message>"), so log entries can be
+	correlated with the JSON sample logs (ServerLogTask/SudLogTask) without
+	relying on journalctl's own timestamps, which aren't present in the
+	mirrored log files themselves."""
 
 	def __init__(self, *streams):
 		self.streams = streams
+		self._at_line_start = True
 
 	def write(self, data):
+		if not data:
+			return
+		out = []
+		for line in data.splitlines(keepends=True):
+			if self._at_line_start:
+				out.append(time.strftime("%Y-%m-%dT%H:%M:%S:", time.localtime()))
+			out.append(line)
+			self._at_line_start = line.endswith('\n')
+		text = ''.join(out)
 		for stream in self.streams:
-			stream.write(data)
+			stream.write(text)
 
 	def flush(self):
 		for stream in self.streams: