engine/kokoro: question doubling + kludges notes

Re-applies the Kokoro-specific hacks that main intentionally
omits:

- _emphasize_questions doubles '?' to '??' so the 82M's flat
  interrogative prosody gets a rising-pitch cue
- engines/kokoro/hacks.md documents this and the other Kokoro-
  tuned bits (gap durations, lowercase-only respellings) with the
  'remove when we move to a bigger model' marker

Deploy from this branch to /srv/appdata/kokoro/build/ when
you want the tuned version. Main's vanilla Kokoro is for
reference / future cleanup.

engines/kokoro/server.py

@@ -113,12 +113,23 @@ def _parse_tag(match: re.Match) -> float:
     return dur / 1000.0 if unit == "ms" else dur
 
 
+# [HACK — engine/kokoro] Kokoro-82M has weak question prosody on a
+# single `?`. Doubling the question mark to `??` reliably triggers a
+# more interrogative rising-pitch contour without changing semantics.
+# Skip if already doubled or part of an interrobang. See hacks.md.
+_QUESTION_RE = re.compile(r"(?<![?!])\?(?!\?)")
+
+
+def _emphasize_questions(text: str) -> str:
+    return _QUESTION_RE.sub("??", text)
+
+
 def _expand_inline(text: str, voice: str | None) -> list[Node]:
     """Expand inline [breath]/[pause]/[scene] tags inside a chunk
     of text that already has a single voice attribution. Voice
     blocks themselves are handled one level up in split_to_nodes."""
     out: list[Node] = []
-    text = text.strip()
+    text = _emphasize_questions(text.strip())
     if not text:
         return out
     cursor = 0