feat(credentials): add Azure OpenAI credential type to the project dashboard

[Rahulkaushik01]

What & why

Adds a per-project Azure OpenAI credential to the project dashboard, alongside the
existing STT providers. This is the storage foundation for upcoming meeting title +
summary generation — a separate concern from the transcription OpenAI credential
(chat/completions needs endpoint + deployment + api-version, which a plain key can't hold).

Scope: dashboard + encrypted storage only. No consumer is wired yet (the summarization
task lands in a later phase), so this changes no runtime behaviour — a project without an
Azure credential is simply unaffected.

How it works

• Fields captured: endpoint, deployment, api_key, api_version (optional → defaults to
  the DEFAULT_AZURE_OPENAI_API_VERSION constant).
• Save/edit: get_or_create(project, type) + set_credentials(dict) — Fernet-encrypted at
  rest, exactly like every other provider (verified: the stored blob is ciphertext, no plaintext).
• Fetch (for the future task): …credentials.filter(credential_type=AZURE_OPENAI).first().get_credentials().
• Delete: handled by the generic DeleteCredentialsView (no type-specific code).
• Mirrors the External Media Storage (multi-field) + ElevenLabs (masked key) partials; non-secret
  fields are pre-filled on edit so editing never silently drops them.

Per-file changes

• bots/models.py — add AZURE_OPENAI = 12 credential type + DEFAULT_AZURE_OPENAI_API_VERSION constant.
• bots/projects_views.py — Azure branch in get_partial_for_credential_type; save branch in
  CreateCredentialsView.post (require endpoint+deployment+api_key → 400, default api_version);
  Azure query + two context keys in ProjectCredentialsView; import the constant.
• bots/templates/projects/partials/azure_openai_credentials.html (new) — Add/Edit card + modal
  (masked key display, htmx save).
• bots/templates/projects/project_credentials.html — include the Azure card.
• bots/migrations/0095_alter_credentials_credential_type.py (new) — additive AlterField for the
  new choice (no data change).
• bots/tests/test_azure_openai_credentials.py (new) — 9 tests.

Testing

• python manage.py makemigrations --check → No changes detected (migration matches the model).
• python manage.py test bots.tests.test_azure_openai_credentials → 9 passed; existing
  test_delete_credentials → 8 passed (no regression).
• ruff check / ruff format --check → clean.
• Manual/browser E2E: Add → card shows masked key + defaulted api-version → stored dict verified →
  delete. Encryption-at-rest confirmed.

Notes

• No new dependencies.
• Secret only ever lives in the encrypted Credentials row — never in code, env, or a bundle.