Fix transcript speaker assignment

[ComputelessComputer]

Summary

• Replace the dead no-participant transcript speaker panel with a searchable picker for session participants, existing contacts, and newly created contacts.
• Link selected contacts to the session before saving the speaker assignment.
• Render saved user assignments after provider speaker hints so assignment scope is stable regardless of hint storage order.
• Avoid invalid button-in-paragraph markup in transcript segment headers.

Tests

• pnpm exec dprint fmt
• pnpm -F @hypr/desktop exec vitest run src/stt/render-transcript.test.ts src/stt/utils.test.ts src/session/components/note-input/transcript/renderer/speaker-assign.test.ts
• pnpm -F @hypr/desktop typecheck

Fixes #4860
Fixes #4960

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Note

Medium Risk
Changes local-store writes for humans/session participants and transcript hint normalization, which affects how speakers render but stays within desktop STT UI—not auth or billing.

Overview
Transcript speaker assignment is reworked so the segment header popover is a searchable picker instead of a session-participants-only list that could show nothing useful.

Users can pick session participants or contacts, filter by name/email, and add a new contact from the search string. Selecting someone links them to the session (mapping_session_participant, manual) when needed, then saves the speaker assignment. Assignments anchor on the first word in the segment that has an id, not blindly words[0].

Rendering applies provider_speaker_index hints on words before building user assignment scopes, so assignment channel/speaker scope stays correct even when hints are stored in the wrong order.

Segment headers use a div instead of p so the assign control is not a button inside a paragraph.

Unit tests cover grouping, create-option deduping, anchor word id, and hint ordering.

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