Auto-migrate (or clearly reject) the pre-#7 config shape

[roziscoding]

Context

#7 changed the config schema:

Before

{
  "indexer": { "priority": 1, "autoRegister": true },
  "servers": {
    "sources": [{ "type": "jellyfin", ... }],
    "peers": [{ ... }],
    "destinations": [{ "type": "radarr", ... }, { "type": "sonarr", ... }]
  }
}

After

{
  "servers": [
    { "type": "radarr", ..., "source": true, "destination": true, "autoregister": { "enable": true, "priority": 1 } }
  ],
  "peers": [{ ... }]
}

AppConfig.parse now throws on an old-shape file (servers is an array, not an object; no indexer block), so anyone upgrading with their existing config gets a hard Zod error at boot with no guidance.

Ask

Detect the legacy shape and migrate it (or, at minimum, fail with a clear, actionable message + a documented mapping). Proposed mapping:

• servers.destinations[] (radarr/sonarr) → servers[] with destination: true.
• servers.sources[] of type jellyfin → dropped, with a warning that Jellyfin sourcing was removed (point at Radarr/Sonarr source: true).
• servers.peers[] → top-level peers[].
• indexer.autoRegister / indexer.priority → per-server autoregister: { enable, priority }.

Implementation ideas: a pre-parse migration step in getAppConfig that recognizes the old shape (e.g. servers is a non-array object) and rewrites it in-memory (optionally writing the migrated file back with a .bak of the original), logging what changed.