feat(podcasts): model registry integration, credential passthrough & new features (#632)

* feat(podcasts): integrate model registry for profiles and credential passthrough

Replace loose provider/model string fields with record<model> references
in podcast profiles, enabling credential passthrough to podcast-creator.

Backend:
- EpisodeProfile: outline_llm, transcript_llm (record<model>) replace
  outline_provider/outline_model strings. New language field (BCP 47).
- SpeakerProfile: voice_model (record<model>) replaces tts_provider/
  tts_model strings. Per-speaker voice_model override support.
- Migration 14: schema changes making legacy fields optional, adding new
  record<model> fields.
- Data migration (migration.py): auto-converts legacy profiles to model
  registry references on startup. Idempotent.
- podcast_commands.py: resolves credentials for ALL profiles before
  calling podcast-creator.
- New /api/languages endpoint (pycountry + babel) with BCP 47 locale
  codes (pt-BR, en-US, etc.).

Frontend:
- Episode/speaker profile forms use ModelSelector instead of manual
  provider/model dropdowns.
- Language dropdown with BCP 47 codes in episode profile form.
- Per-speaker TTS voice model override in speaker profile form.
- "Templates" tab renamed to "Profiles".
- Setup required badge on unconfigured profiles.
- i18n updated across all 8 locales.

Closes #486, closes #552

* fix(i18n): remove unused legacy podcast provider/model keys

Remove 10 orphaned i18n keys across all 8 locales that were left behind
after replacing manual provider/model dropdowns with ModelSelector.

* fix: address review violations in podcast model registry

- P1: Remove profiles with failed model resolution from dicts to prevent
  podcast-creator validation errors on unrelated profiles
- P2: Use centralized QUERY_KEYS.languages instead of inline key
- P3: Fix ISO 639-1 → BCP 47 in model field description and CLAUDE.md
- P3: Update "templates" → "profiles" in locale string values (all 8)

* chore: bump version to 1.8.0

open_notebook/database/async_migrate.py

@@ -115,6 +115,9 @@ class AsyncMigrationManager:
             AsyncMigration.from_file(
                 "open_notebook/database/migrations/13.surrealql"
             ),
+            AsyncMigration.from_file(
+                "open_notebook/database/migrations/14.surrealql"
+            ),
         ]
         self.down_migrations = [
             AsyncMigration.from_file(
@@ -156,6 +159,9 @@ class AsyncMigrationManager:
             AsyncMigration.from_file(
                 "open_notebook/database/migrations/13_down.surrealql"
             ),
+            AsyncMigration.from_file(
+                "open_notebook/database/migrations/14_down.surrealql"
+            ),
         ]
         self.runner = AsyncMigrationRunner(
             up_migrations=self.up_migrations,