feat(api): add skip_arr_notification option to POST /import/file

[javi11]

Summary

• Adds skip_arr_notification boolean field (default false) to the POST /import/file request body — callers that set it to true suppress ARR notifications for that specific import
• When the flag is set the handler encodes {"skip_arr_notification":true} into ImportQueueItem.Metadata using the existing JSON metadata pattern (same approach as nzbdav_id, extracted_files)
• The post-import coordinator checks the flag in HandleSuccess before calling notifyARRWith; a skipped notification is logged at DEBUG with queue_id and path

What changed

File	Change
internal/api/types.go	SkipArrNotification bool added to ManualImportRequest (omitempty → backward-compatible)
internal/api/import_handlers.go	Encodes flag into queue item metadata; warns via slog if marshal fails
internal/api/import_handlers_skip_arr_test.go	Unit tests for encoding logic
internal/importer/postprocessor/coordinator.go	shouldSkipARRNotification helper + HandleSuccess wiring
internal/importer/postprocessor/coordinator_skip_arr_test.go	6-case unit test for helper + integration test for HandleSuccess skip path

No database migration needed — uses the pre-existing Metadata *string JSON field.

Test Plan

• go test ./... -race passes (all packages green)
• POST /import/file with "skip_arr_notification": false (or omitted) — ARR notification fires as before
• POST /import/file with "skip_arr_notification": true — logs ARR notification skipped (requested by caller) at DEBUG, no ARR scan triggered

[lostgit]

btw, with ARR service engine set to off, I still see

{"log":"time=2026-04-18T16:17:02.427-04:00 level=DEBUG msg=\"Could not find specific ARR instance for file, broadcasting scan\" component=postprocessor path=/mnt/fuse/complete/Movies/<snip> error=\"no ARR instance found managing file path: /mnt/fuse/complete/Movies/<snip>\"\n","stream":"stdout","time":"2026-04-18T20:17:02.427573422Z"}

[javi11]

Ok will tackle that in another pr