feat(settings): storage budgets and retention in settings UI, tmdbMaxSize default 5000 (INT-3)

- Automation section gets storage budget, retention and cache TTL cards bound to settings.storage
- Metadata section drops deprecated cache.tmdbTtlHours / cache.emptyResultTtlSec / identity.poolArchiveDays inputs
- cache.tmdbMaxSize default 256 -> 5000; migration 0051 bumps stored values still at the old default

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/porting/moviepilot-tmdb-cache.md

@@ -23,7 +23,7 @@ PG 读写失败时 TMDB 路径按未命中处理(内存缓存不会失败)。
 
 | 上游 | 我们 |
 |---|---|
-| `maxsize = CONF.tmdb`(256;大内存 1024) | 设置 `cache.tmdbMaxSize`(缺省 256) |
+| `maxsize = CONF.tmdb`(256;大内存 1024) | 设置 `cache.tmdbMaxSize`(缺省 5000,存 PG 不受进程内存约束) |
 | `ttl = CONF.meta = META_CACHE_EXPIRE 小时`(缺省 24) | CACHE-2 起按请求类别取设置:`/search/`、`/find/` 用 `storage.cacheTtl.tmdbSearchDays`(7 天),其余用 `tmdbDetailDays`(30 天) |
 | `empty_ttl = EMPTY_RESULT_CACHE_TTL`(1800 秒),`empty_if = results 为空列表` | `storage.cacheTtl.tmdbMissDays`(1 天);`isEmptyResult` 同判定 |
 | `skip_none`(连接失败不缓存)、`skip_if = success:false`(业务失败不缓存) | 这两类在 `fetchWithRetry` 抛错,不会写缓存 |