docs: document Seerr requester in pre-deletion warnings and webhook mediaItems field

[Copilot]

Docs drift update for the next Maintainerr release, covering the feat(notifications): name the Seerr requester in the pre-deletion warning change (#3270).

Changes

• Notifications.md — notification types table: Updated "Media About to be Handled" row to note that Seerr requester info is included when Seerr is configured. Added a note block with full behavioral detail: season-aware lookup, best-effort, silently omitted if Seerr is unreachable or the item was not requested there.

• Notifications.md — webhook variables section: Expanded the sparse {{extra}} entry into an extra-fields table documenting collectionName, dayAmount, and mediaItems. Added a mediaItems example showing the new requestedBy array:

  [
    { "mediaServerId": "abc123", "requestedBy": ["alice"] },
    { "mediaServerId": "def456" }
  ]

• Configuration.md — Seerr section: Widened the description to include pre-deletion notification requesters alongside rule parameters and request removal.

Intentionally skipped

Commit	Reason
a25bd68 fix: Media Handled title	Bug fix; notification type description remains accurate
398a1c3 fix: Tautulli sw_lastWatched threshold	Restores correct behavior; no config or UI changes
074ff57 fix: Jellyfin season cache TTL	Internal cache fix; no observable surface for users to configure
a3914bd fix: Plex prefetch progress logging	Log-only improvement

[enoch85]

@copilot Please fix code formatting and quality checks

[Copilot]

@copilot Please fix code formatting and quality checks

Fixed in the latest commit — ran prettier --write on the changed files and all pass prettier --check now.