fix(skills): pipeline fixes from prompt-guide validation (BGM, caption accent, voice, PR version)

Behavior fixes surfaced by the prompt-guide validation campaign (Tier 1+2
of the upstream bug list; Tier 3 tracked in #2107). Split out from the
doc-only updates, which follow in a separate PR.

- BGM level: default bed volume under narration was 0.8 linear (~-2 dB,
  ~16 dB too hot vs voice). Now 0.12 (~-18 dB) via shared
  bgmDefaultVolume() in media-use bgm.mjs + assemble-index fallbacks in
  faceless-explainer / pr-to-video / product-launch-video. Explicit
  volume still wins; silent-film 0.9 and music-to-video unchanged.
  Adds bgm.test.mjs (3 cases); bgm.md reference updated to match.
- Caption accent: semanticColors() ranked accents purely by chroma, so a
  preserved status red (#dc2626) outranked the brand accent and captions
  highlighted in error-red. Status-keyed colors now excluded via shared
  STATUS_ROLE_KEY regex consumed by both tokens.mjs and build-frame.mjs
  (all three skill copies kept in sync).
- Voice threading: workflow SKILL.md Step 3.1 blocks now instruct
  choosing the narration voice from the user's ask and passing
  --voice <id>; previously "a male voice" was silently ignored and the
  default (Marcia/am_michael) always won.
- fetch-pr shipping version: MERGED PRs get best-effort shipped_version
  + version_source in pr.json (first release published at/after merge,
  else default-branch package.json marked unreleased); ingest surfaces
  it as a 'Shipped in:' brief line; story-design.md forbids inventing
  versions when absent.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

skills/product-launch-video/scripts/lib/tokens.mjs

@@ -48,6 +48,14 @@ export const UA_DEFAULT_COLORS = new Set(
   ["#0000EE", "#0000FF", "#0000CC", "#1A0DAB", "#551A8B", "#EE0000"].map((c) => c.toUpperCase()),
 );
 
+// Semantic STATUS roles (green "positive", red "negative"/"error", amber "warning" …). Their HUE
+// carries the meaning, so they are never a brand ACCENT — a status red is frequently the most
+// chromatic color in a palette (e.g. #dc2626 chroma 182 beats a deep-blue accent #1E40AF chroma
+// 145) and would otherwise win a pure chroma ranking, painting captions/highlights the error red.
+// build-frame.mjs uses this same key set to protect status colors during the preset→brand remix.
+export const STATUS_ROLE_KEY =
+  /(?:^|[-_])(?:positive|negative|success|error|warning|danger|good|bad|up|down)(?:[-_]|$)/i;
+
 // Pick the brand ACCENT — never by raw chroma alone, never a UA-default link color.
 // Priority:
 //   1) with capture colorStats → the colorful color that RECURS across the UI. The brand
@@ -134,7 +142,8 @@ export function brandRolesFromStats(stats, colorsInOrder) {
 // Map a list of [key, value] colors to semantic roles. ink = a dark/ink-named
 // color (else darkest); canvas = a paper/cream/white-named color (else lightest);
 // accents = whatever's left, ranked by chroma (the loudest color is almost always
-// the brand accent) — UA-default link colors excluded so a stray <a> color never wins.
+// the brand accent) — UA-default link colors AND semantic status colors (positive/
+// negative/error…) excluded so neither a stray <a> color nor a status red ever wins.
 // For an unkeyed brand list, pass synthetic keys — name matching simply no-ops and it
 // falls back to luminance/chroma, which is what we want. NOTE: when capture colorStats
 // exist, prefer brandRolesFromStats() — it picks by function, not these proxies.
@@ -154,7 +163,13 @@ export function semanticColors(colors) {
     byLum[byLum.length - 1] ?? colors[colors.length - 1],
   );
   const accents = colors
-    .filter(([, v]) => v !== ink && v !== canvas && !UA_DEFAULT_COLORS.has(String(v).toUpperCase()))
+    .filter(
+      ([k, v]) =>
+        v !== ink &&
+        v !== canvas &&
+        !UA_DEFAULT_COLORS.has(String(v).toUpperCase()) &&
+        !STATUS_ROLE_KEY.test(k), // a status red/green carries meaning by hue — never an accent
+    )
     .sort((a, b) => chroma(b[1]) - chroma(a[1]))
     .map(([, v]) => v);
   return { ink, canvas, accent: accents[0] ?? ink, accent2: accents[1] ?? accents[0] ?? ink };