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/services/transcript_process.py

@@ -7,7 +7,7 @@ This module provides result-based error handling that works in both contexts:
 """
 
 from dataclasses import dataclass
-from typing import Literal, Union
+from typing import Literal, Union, assert_never
 
 import celery
 from celery.result import AsyncResult
@@ -18,7 +18,6 @@ from reflector.pipelines.main_file_pipeline import task_pipeline_file_process
 from reflector.pipelines.main_multitrack_pipeline import (
     task_pipeline_multitrack_process,
 )
-from reflector.utils.match import absurd
 from reflector.utils.string import NonEmptyString
 
 
@@ -155,7 +154,7 @@ def dispatch_transcript_processing(config: ProcessingConfig) -> AsyncResult:
     elif isinstance(config, FileProcessingConfig):
         return task_pipeline_file_process.delay(transcript_id=config.transcript_id)
     else:
-        absurd(config)
+        assert_never(config)
 
 
 def task_is_scheduled_or_active(task_name: str, **kwargs):