fix(exclusions): fail safe when JustWatch or Trakt are unavailable

[rfsbraz]

• JustWatch API failures (timeout, rate limit, network errors) were swallowed into empty search results, so available_on exclusions silently stopped firing during outages and items the user wanted protected proceeded toward deletion. _search now raises JustWatchError so callers can tell a service failure apart from a genuine not-found, and check_excluded_justwatch fails safe by skipping the item for that run with a warning.
• Trakt list fetch failures were caught and returned as an empty list, silently disabling configured Trakt exclusion lists. _fetch_list_items now raises TraktError, and the per-library processing in deleterr catches it, logs prominently, and skips the library entirely (no deletions) for that run.
• Added unit tests covering both fail-safe paths: JustWatch errors exclude the item and log a warning, and a Trakt outage marks the library as failed without deleting anything.

[github-actions]

🐳 To test this PR, build and run directly from the branch:

Using docker compose:

services:
  deleterr:
    build: https://github.com/rfsbraz/deleterr.git#refs/pull/283/head
    volumes:
      - ./config:/config
    environment:
      LOG_LEVEL: DEBUG

Using docker build:

docker build https://github.com/rfsbraz/deleterr.git#refs/pull/283/head -t deleterr:pr-283
docker run --rm -v ./config:/config -e LOG_LEVEL=DEBUG deleterr:pr-283

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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