fix(visualizer): bars recover after far-forward seeks into undecoded audio

ensureDecodeAround let a running decode pass close ANY forward gap in
place — at 4x pacing, skipping 30 min ahead meant ~7.5 min for the
frontier to arrive: bars held their last frame indefinitely. Now a gap
beyond 15s restarts the pass at the seek target (network coverage there
in ~1.6s, verified); smaller gaps close in place (cheaper than a
reconnect + range request). Seek-key holds are debounced (400ms) so
rapid re-seeks don't reconnect-spam the stream's server, and pending
seek-decode cancels on pause/stop so no ffmpeg restarts while paused.

Also fixes a pre-existing config-write race that intermittently failed
visualizer-toggle.test.ts: updateConfig re-resolved the config path and
re-read the patch state when the deferred write-chain drained, so a
queued save could land in a directory XDG_CONFIG_HOME had since been
pointed at (or carry state mutated after queueing). Path and patch
snapshot are now captured eagerly at call time.

tests/audio-pcm-cache.test.ts

@@ -97,6 +97,55 @@ function tmpWav(): string {
 }
 
 const hasFfmpeg = !!Bun.which("ffmpeg");
+
+test.skipIf(!hasFfmpeg)(
+	"far-forward seek into undecoded territory restarts decode AT the target (bars recover in seconds, not minutes)",
+	async () => {
+		const wav = tmpWav();
+		writeSineWav(wav, 60);
+		const cache = new EpisodePcmCache({ url: wav });
+		try {
+			cache.startDecode(0);
+			await waitForCoverage(cache, 1);
+
+			// Skipping 45s ahead while the pass still crawls at 4x must restart
+			// the segment at the target — waiting for the frontier to chew
+			// through the skipped region is minutes of frozen bars.
+			cache.ensureDecodeAround(45);
+			expect(cache.decoding).toBe(true);
+			expect(cache.activeDecodeBaseSec).toBe(45);
+			await waitForCoverage(cache, 45.1);
+		} finally {
+			cache.stop();
+			await Bun.$`rm -f ${wav}`.quiet();
+		}
+	},
+	{ timeout: 20000 },
+);
+
+test.skipIf(!hasFfmpeg)(
+	"small forward gap closes in place — no needless reconnect",
+	async () => {
+		const wav = tmpWav();
+		writeSineWav(wav, 60);
+		const cache = new EpisodePcmCache({ url: wav });
+		try {
+			cache.startDecode(0);
+			await waitForCoverage(cache, 2);
+
+			// ~5s past the running frontier: at 4x pacing this closes in ~1.5s,
+			// cheaper than a reconnect — the pass must NOT restart.
+			const target = cache.coverageEndSec + 5;
+			cache.ensureDecodeAround(target);
+			expect(cache.activeDecodeBaseSec).toBe(0);
+			await waitForCoverage(cache, target);
+		} finally {
+			cache.stop();
+			await Bun.$`rm -f ${wav}`.quiet();
+		}
+	},
+	{ timeout: 20000 },
+);
 const FIVE_SEC_BASE = 5 * SAMPLE_RATE; // decode offset for position-mapping tests
 
 test.skipIf(!hasFfmpeg)(