Audio: robust rate estimation + color-coded log levels

Harden the guessed-stream sample-rate measurement that produced wrong rates
(e.g. 44100 read as ~46205). New rate_estimator.hpp measures over longer
~0.5 s windows, rejects any window that doesn't snap to a standard rate
(standard rates are >8% apart, so a quantization/burst error big enough to
miss one lands in no-man's-land, never on a wrong neighbour), and requires
consensus across windows before committing. If consensus isn't reached it
commits a low-confidence estimate (new AudioFormat_LowConfidence, shown red)
rather than spinning or publishing garbage. Pure logic, unit-tested with
adversarial cadences (rate_estimator_test) incl. the real 46205 bug value.

Add log severity levels: hook logw/loge set LogRecord.level; the host Log
window colors warnings amber and errors red. The low-confidence rate logs a
warning. Protocol -> v15 (new format states); also reserves AudioFormat_Override.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

host/src/log_panel.hpp

@@ -25,7 +25,12 @@ public:
 private:
 	void add_line(const LogRecord& rec);
 
-	std::deque<std::string> lines_;
+	struct Line
+	{
+		std::string text;
+		std::uint32_t level; // LogLevel, for colouring
+	};
+	std::deque<Line> lines_;
 	char filter_[96] = {};
 	bool autoscroll_ = true;
 	std::uint64_t first_millis_ = 0; // hook clock at the first line, for relative timestamps