feat: add transcript format parameter to GET endpoint (#709)

* feat: add transcript format parameter to GET endpoint

Add transcript_format query parameter to /v1/transcripts/{id} endpoint
with support for multiple output formats using discriminated unions.

Formats supported:
- text: Plain speaker dialogue (default)
- text-timestamped: Dialogue with [MM:SS] timestamps
- webvtt-named: WebVTT subtitles with participant names
- json: Structured segments with full metadata

Response models use Pydantic discriminated unions with transcript_format
as discriminator field. POST/PATCH endpoints return GetTranscriptWithParticipants
for minimal responses. GET endpoint returns format-specific models.

* Copy transcript format

* Regenerate types

* Fix transcript formats

* Don't throw inside try

* Remove any type

* Toast share copy errors

* transcript_format exhaustiveness and python idiomatic assert_never

* format_timestamp_mmss clear type definition

* Rename seconds_to_timestamp

* Test transcript format with overlapping speakers

* exact match for vtt multispeaker test

---------

Co-authored-by: Sergey Mankovsky <sergey@monadical.com>
Co-authored-by: Igor Loskutov <igor.loskutoff@gmail.com>

server/reflector/views/transcripts_process.py

@@ -1,4 +1,4 @@
-from typing import Annotated, Optional
+from typing import Annotated, Optional, assert_never
 
 from fastapi import APIRouter, Depends, HTTPException
 from pydantic import BaseModel
@@ -15,7 +15,6 @@ from reflector.services.transcript_process import (
     prepare_transcript_processing,
     validate_transcript_for_processing,
 )
-from reflector.utils.match import absurd
 
 router = APIRouter()
 
@@ -44,7 +43,7 @@ async def transcript_process(
     elif isinstance(validation, ValidationOk):
         pass
     else:
-        absurd(validation)
+        assert_never(validation)
 
     config = await prepare_transcript_processing(validation)