fix: Preserve Captain LLM defaults (#14858)

# Pull Request Template

## Description

Adjusts the Captain LLM feature defaults after feature routing so the
defaults stay intentional and avoid unintended high-cost model upgrades.
Assistant, copilot, and onboarding content generation now default to
`gpt-4.1`; audio transcription keeps `gpt-4o-mini-transcribe` as the
default while exposing `whisper-1` as an available account override
option.

Related: https://linear.app/chatwoot/issue/CW-7425/test-new-models

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)

## How Has This Been Tested?

- `ruby -ryaml -e 'yaml = YAML.load_file("config/llm.yml"); features =
yaml.fetch("features"); models = yaml.fetch("models"); features.each {
|name, cfg| missing = Array(cfg["models"]) - models.keys; raise
"#{name}: missing #{missing.join(",")}" if missing.any?; raise "#{name}:
default not in models" unless
Array(cfg["models"]).include?(cfg["default"]) }'`
- `node -e
"JSON.parse(require('fs').readFileSync('app/javascript/dashboard/i18n/locale/en/settings.json',
'utf8'))"`
- `pnpm exec prettier --check
app/javascript/dashboard/i18n/locale/en/settings.json`
- `bundle exec rspec spec/lib/llm/feature_router_spec.rb
spec/enterprise/services/llm/base_ai_service_spec.rb
spec/enterprise/models/concerns/agentable_spec.rb
spec/enterprise/services/messages/audio_transcription_service_spec.rb
spec/models/concerns/captain_featurable_spec.rb
spec/models/account_spec.rb
spec/controllers/api/v1/accounts/captain/preferences_controller_spec.rb
spec/controllers/super_admin/accounts_controller_spec.rb`
- `bundle exec rspec
spec/enterprise/services/captain/llm/article_translation_service_spec.rb
spec/enterprise/services/messages/audio_transcription_service_spec.rb
spec/enterprise/services/llm/base_ai_service_spec.rb`
- `RUBOCOP_CACHE_ROOT=/private/tmp/rubocop_cache bundle exec rubocop
enterprise/app/services/captain/llm/article_translation_service.rb
enterprise/app/services/messages/audio_transcription_service.rb
spec/enterprise/services/captain/llm/article_translation_service_spec.rb
spec/enterprise/services/llm/base_ai_service_spec.rb
spec/enterprise/services/messages/audio_transcription_service_spec.rb`
- `git diff --check`

## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

app/javascript/dashboard/i18n/locale/en/settings.json

@@ -440,7 +440,9 @@
       "DESCRIPTION": "Enable or disable AI-powered features.",
       "AUDIO_TRANSCRIPTION": {
         "TITLE": "Audio Transcription",
-        "DESCRIPTION": "Automatically convert voice messages and call recordings into searchable text transcripts."
+        "DESCRIPTION": "Automatically convert voice messages and call recordings into searchable text transcripts.",
+        "MODEL_TITLE": "Audio Transcription Model",
+        "MODEL_DESCRIPTION": "Select the AI model to use for converting audio messages into text transcripts"
       },
       "HELP_CENTER_SEARCH": {
         "TITLE": "Help Center Search Indexing",