fix: address round 3 review feedback

Blocking issues:
1. Restore ntfy regression tests (3 tests + ModuleType import) accidentally
   dropped during first commit's merge onto main.
2. QQBot raw OpenID fallback: directory miss for ASCII targets now falls
   back to raw ID instead of erroring. Non-ASCII display names still error.
   E2E tests cover: raw OpenID fallback, display-name precedence, non-ASCII rejection.
3. MP3/FLAC removed from _QQBOT_VOICE_EXTS (.silk/.wav only). MP3 now routes
   as MEDIA_TYPE_FILE for C2C; groups reject with 'document not supported'.

Test quality:
4. Strengthened test_accept_file_under_limit: now verifies upload actually
   happened (not just absence of 'too large' error).
5. Added 9 protocol-level tests (TestQqbotProtocolLevel): upload URL,
   upload body fields, message body fields, C2C-to-group fallback,
   group document rejection, multiple media, long caption overflow,
   upload failure propagation, message failure propagation.
6. Added 3 E2E tests (TestQqbotOpenIdFallback): raw OpenID fallback,
   display-name precedence, non-ASCII rejection.

Other:
7. Updated _MAX_QQBOT_INLINE_UPLOAD_BYTES comment: clarifies the 10 MB
   limit is on the base64 JSON body (~7.5 MB raw file).
8. file:// HTML image extraction: confirmed out of scope (main doesn't
   support it either). Tracked in #26041.

Tests: 162 passed, 0 failed.

Author: KK