feat(cloud-sync): add Nuvio and MDBList providers

[moodiness]

Summary

Supersedes #68, which GitHub closed automatically when its source branch was renamed from feat/nuvio-provider to feat/cloud-sync-providers.

Adds Nuvio Cloud and MDBList as first-class Scrob synchronization providers, and includes the Trakt watched-history pagination fix reviewed in #68.

Nuvio Cloud

• authenticate with Nuvio email/password without persisting the password
• persist and rotate the Nuvio refresh token
• load named Nuvio profiles and synchronize each profile independently
• pull library items, watched history, and Continue Watching progress
• push watched/unwatched state and playback progress back to Nuvio
• normalize inbound IMDb identifiers through TMDB
• resolve outbound TMDB identifiers to Nuvio-compatible bare IMDb IDs
• support manual Sync now, explicit Push, and scheduled Auto Pull
• support 15m, 30m, 1h, 3h, 6h, 12h, 24h, and 48h Nuvio pull intervals
• include directly collected cloud series in My Shows

MDBList

• authenticate with the per-user API key from MDBList Preferences
• validate the key through the connection-status endpoint before storage
• pull watched history, ratings, and watchlist items on demand
• push full watched, ratings, and managed-watchlist snapshots on demand
• push individual watched, rating, and managed-watchlist edits as they happen
• persist the currently selected MDBList options automatically before Pull or Push, without requiring a separate Save Changes action
• fan inbound MDBList watched/rating changes out to other enabled providers without echoing them back to MDBList
• follow cursor pagination with the documented 1,000-item maximum and support legacy offset pagination
• batch outbound payloads without constructing a second full payload copy
• resolve show IMDb/TVDB identifiers to TMDB once per pull and cache the result for the job
• preserve watch and rating timestamps
• expose MDBList jobs through the existing sync-status UI
• keep MDBList pull manual; no automatic MDBList scheduler or interval setting

Additional fixes

• request Trakt's documented maximum page size and follow X-Pagination-Page-Count
• request extended=progress on every watched-show page so episode data is retained
• make Trakt and Simkl Disconnect buttons use the same destructive red treatment as connection deletion
• clarify that Scrob expects a TMDB Read Access Token

Database

Adds one Alembic revision with:

• seven MDBList user settings: API key plus three pull and three push flags
• lists.mdblist_slug for the managed MDBList watchlist
• the mdblist collection-source enum value

No MDBList automatic-pull column is created.

Verification

• python -m compileall -q .
• python -m unittest tests.test_trakt tests.test_nuvio tests.test_mdblist -v — 19 tests passed
• npm run build — passed
• Docker image rebuilt and /health returned 200
• clean database upgraded from the initial migration through the new Alembic head; seven MDBList settings present and no automatic-pull column
• live MDBList pull completed successfully through the local Scrob UI
• live reversible MDBList smoke test added, read back, and removed a watched item, rating, and watchlist item; cleanup confirmed all three absent
• live MDBList season response confirmed episode expansion and nested show identifiers
• reproduced the unsaved-option Push failure (400), then verified automatic preference persistence (PATCH 200) followed by successful Push and Pull job creation (POST 200)
• browser check confirmed the MDBList Pull control remains available, Automatic pull is absent, and Disconnect uses the red destructive hover style

Nuvio API documentation: https://nuvio.tv/docs

MDBList API documentation: https://api.mdblist.com/docs/

Closes #71
Fixes #61