feat(player): click-to-seek progress bar; 2-row waveform bars with peak normalization

- ProgressBar: full-width played/remaining bar in the player pane, click-to-seek;
  waveform no longer handles seeking or the played/future color split (pure visual)
- bars: 2 terminal rows per bar (16 levels) via barChars, partial block in the
  top row so the column renders continuously
- fix bars maxing at audio start: disable cava autosens (silence gain-ramp),
  pre-warm the malloc'd FFT window with zeros, skip partial FFT windows
- createBarScaler peak follower + power curve replaces cava autosens for
  level-to-height mapping (src/utils/bar-mapping.ts, unit-tested)

src/utils/bar-mapping.ts

@@ -0,0 +1,102 @@
+/**
+ * Pure bar-scaling helpers for the terminal waveform.
+ *
+ * barChars maps a 0..16 level to the two characters of a 2-row bar built
+ * from Unicode lower block elements (U+2581..U+2588). The partial block
+ * sits in the TOP row (its glyph bottom edge = row bottom), so a full
+ * block below makes a visually continuous 2-cell column — the "double the
+ * default height" requirement (each bar = 2 terminal rows, 16 heights).
+ *
+ * createBarScaler is a stateful fast-attack / slow-release peak follower
+ * that replaces cava's autosens: a loud start cannot pin every bar at
+ * full height (the peak follower absorbs it) and quiet content gets
+ * normalized up.
+ */
+
+// ── Types ────────────────────────────────────────────────────────────
+
+export interface BarScalerOptions {
+	/** Peak follower decay per frame (default: 0.985) */
+	release?: number;
+	/** Power curve applied after normalization (default: 0.7) */
+	curve?: number;
+	/** Silence threshold — below this the input is treated as silent (default: 1e-6) */
+	epsilon?: number;
+}
+
+// ── Constants ────────────────────────────────────────────────────────
+
+/** Number of discrete bar heights (2 rows × 8 block levels). */
+export const BAR_LEVELS = 16;
+
+/** Lower block elements, index 0 = space (silence) through full block (max). */
+const LOWER = [
+	" ",
+	"\u2581",
+	"\u2582",
+	"\u2583",
+	"\u2584",
+	"\u2585",
+	"\u2586",
+	"\u2587",
+	"\u2588",
+];
+
+// ── Bar mapping ──────────────────────────────────────────────────────
+
+/**
+ * Map a bar level (0..16) to the two characters that render it as a
+ * 2-row column: top row + bottom row.
+ *
+ * level 0        → { top: " ", bottom: " " }
+ * level 1..8     → { top: " ", bottom: LOWER[level] }
+ * level 9..16    → { top: LOWER[level - 8], bottom: "\u2588" }
+ */
+export function barChars(level: number): { top: string; bottom: string } {
+	const raw = Math.floor(level);
+	const lvl = Number.isFinite(raw)
+		? Math.max(0, Math.min(BAR_LEVELS, raw))
+		: 0;
+
+	if (lvl === 0) return { top: " ", bottom: " " };
+	if (lvl <= 8) return { top: " ", bottom: LOWER[lvl] };
+	return { top: LOWER[lvl - 8], bottom: "\u2588" };
+}
+
+// ── Peak-follower scaler ─────────────────────────────────────────────
+
+const clamp01 = (value: number): number => Math.max(0, Math.min(1, value));
+
+/**
+ * Create a stateful bar scaler. Each call normalizes its input against a
+ * peak follower (instant attack, multiplicative release), then applies a
+ * power curve so low-energy content remains visible. Returns a new
+ * number[] per call.
+ */
+export function createBarScaler(
+	opts?: BarScalerOptions,
+): (values: ArrayLike<number>) => number[] {
+	const release = opts?.release ?? 0.985;
+	const curve = opts?.curve ?? 0.7;
+	const epsilon = opts?.epsilon ?? 1e-6;
+	let peak = 0;
+
+	return (values: ArrayLike<number>): number[] => {
+		let frameMax = 0;
+		for (let i = 0; i < values.length; i++) {
+			const magnitude = Math.abs(values[i]);
+			if (magnitude > frameMax) frameMax = magnitude;
+		}
+
+		// Fast attack, slow release
+		peak = frameMax > peak ? frameMax : peak * release;
+
+		const gain = peak > epsilon ? 1 / peak : 0;
+
+		const output = new Array<number>(values.length);
+		for (let i = 0; i < values.length; i++) {
+			output[i] = Math.pow(clamp01(values[i] * gain), curve);
+		}
+		return output;
+	};
+}