* feat(server): expand mixed English completion choices
* fix(server): count fixed English in the first-page English budget
- Fixed-position English never takes the slot, regardless of
first_page_count; fixed English on the first page counts toward the
budget and the page room, and the first-page emoji is placed so that
re-inserting fixed words returns it to the last slot.
- SlottedEnglishIndex returns the first unfixed English, so slot
learning keeps working when the top-ranked English is fixed.
- Drop the protected-prefix lower bound on the completion target: it
pushed the single default completion off the first page.
- Protect cloud/AI (and AI following English) from the extra English
even with a learned slot.
- Keep the legacy five-row prefix query for the default single English
candidate; only first_page_count > 1 uses the mixed distinct-word query.
- Let SetConfiguredEnglishMixedInputFirstPageCount own the range check.
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Co-authored-by: li shiyan <150001555+lsy9966303@users.noreply.github.com>
Lu Fan(SonnyCalcr)