Generate provisional dictation audio so dictée missions can be played

Manual testing confirmed the "La clairière de l'écho" dictée mission
was unplayable: no audio file existed yet (decisions.md point 8), so
there was nothing to listen to before transcribing the sentence.

Adds tools/generate_dictation_audio.py (offline eSpeak NG synthesis +
ffmpeg encoding to Ogg Vorbis, exposed as `make
generate-dictation-audio`) and uses it to generate
ce1_accord_adjectif_dictee_01.ogg. A new headless test
(tests/data/test_dictation_audio.gd) guards against future dictées
being added without regenerating their audio.

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

tools/generate_dictation_audio.py

@@ -0,0 +1,118 @@
+#!/usr/bin/env python3
+"""Genere l'audio provisoire des dictees a partir de `data/dictations/*.json`.
+
+Synthese vocale hors ligne (eSpeak NG) + encodage en Ogg Vorbis (ffmpeg), tel
+que decide dans docs/specs/decisions.md, point 8. Ne tourne jamais a
+l'execution du jeu : c'est un outil de redaction de contenu, lance a la main.
+Ne regenere pas un fichier deja present, sauf avec --force.
+"""
+
+from __future__ import annotations
+
+import argparse
+import json
+import shutil
+import subprocess
+import tempfile
+from pathlib import Path
+from typing import Any
+
+REPO_ROOT = Path(__file__).resolve().parent.parent
+DICTATIONS_DIR = REPO_ROOT / "data" / "dictations"
+AUDIO_DIR = REPO_ROOT / "assets" / "audio" / "dictations"
+
+ESPEAK_VOICE = "fr-fr"
+ESPEAK_SPEED_WPM = "135"
+
+
+def _require_tool(name: str, install_hint: str) -> str:
+    path = shutil.which(name)
+    if path is None:
+        raise SystemExit(f"'{name}' introuvable dans le PATH. {install_hint}")
+    return path
+
+
+def load_dictations() -> list[dict[str, Any]]:
+    return [
+        json.loads(path.read_text(encoding="utf-8"))
+        for path in sorted(DICTATIONS_DIR.glob("*.json"))
+    ]
+
+
+def generate_one(espeak_bin: str, ffmpeg_bin: str, dictation: dict[str, Any]) -> Path:
+    audio_id: str = dictation["audio_id"]
+    target_text: str = dictation["target_text"]
+    output_path = AUDIO_DIR / f"{audio_id}.ogg"
+
+    with tempfile.TemporaryDirectory() as tmp_dir:
+        tmp_wav = Path(tmp_dir) / f"{audio_id}.wav"
+        subprocess.run(
+            [
+                espeak_bin,
+                "-v",
+                ESPEAK_VOICE,
+                "-s",
+                ESPEAK_SPEED_WPM,
+                "-w",
+                str(tmp_wav),
+                target_text,
+            ],
+            check=True,
+        )
+        subprocess.run(
+            [
+                ffmpeg_bin,
+                "-y",
+                "-loglevel",
+                "error",
+                "-i",
+                str(tmp_wav),
+                "-c:a",
+                "libvorbis",
+                "-qscale:a",
+                "4",
+                str(output_path),
+            ],
+            check=True,
+        )
+    return output_path
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument(
+        "--force",
+        action="store_true",
+        help="Regenere meme les fichiers deja presents.",
+    )
+    args = parser.parse_args()
+
+    espeak_bin = _require_tool(
+        "espeak-ng",
+        "A installer via le gestionnaire de paquets du systeme (ex. "
+        "`sudo apt install espeak-ng` sous Debian/Ubuntu, `brew install espeak-ng` sous macOS).",
+    )
+    ffmpeg_bin = _require_tool("ffmpeg", "A installer via le gestionnaire de paquets du systeme.")
+
+    AUDIO_DIR.mkdir(parents=True, exist_ok=True)
+
+    generated: list[str] = []
+    skipped: list[str] = []
+    for dictation in load_dictations():
+        if not dictation.get("audio_provisional", False):
+            continue
+        audio_id: str = dictation["audio_id"]
+        output_path = AUDIO_DIR / f"{audio_id}.ogg"
+        if output_path.exists() and not args.force:
+            skipped.append(audio_id)
+            continue
+        generate_one(espeak_bin, ffmpeg_bin, dictation)
+        generated.append(audio_id)
+
+    print(f"Audio genere : {len(generated)} fichier(s) ({', '.join(generated) or 'aucun'}).")
+    if skipped:
+        print(f"Deja present, ignore (--force pour regenerer) : {', '.join(skipped)}.")
+
+
+if __name__ == "__main__":
+    main()