The keepalive could fire for a new turn's context before that context's
voice_settings context-init was sent, making the keepalive the context's
first message (no voice_settings) and causing ElevenLabs to reject the
later init with a 1008 policy violation. The keepalive now only targets a
context once its context-init has been sent (tracked in _context_init_sent).
PR #4344 unconditionally switched to normalizedAlignment to fix garbled
words with pronunciation dictionaries (#4316). But normalizedAlignment
returns the post-normalized form of what was spoken - including
romanization of non-Latin scripts (Chinese rendered as pinyin), which
ends up in the LLM context and degrades subsequent turns.
Gate the switch on pronunciation_dictionary_locators being configured.
Adds a _select_alignment helper with preferred-with-fallback (both
fields are nullable per the API schema), used by both the WebSocket
and HTTP services. Tests cover dictionary mode, default mode, fallback
when preferred is missing or null, and HTTP field-name variants.
