chore: remove obsolete APIs (register, probe, n8n, videos, people)

- Remove /api/v1/register (replaced by /api/v1/files/register)
- Remove /api/v1/probe (replaced by /api/v1/files/:uuid)
- Remove /api/v1/n8n/... (n8n workflow only)
- Remove /api/v1/unregister (high risk)
- Remove /api/v1/videos list (replaced by /api/v1/files)
- Remove /api/v1/people (merged into /api/v1/identities)
- Clean up dead code and unused structs

src/core/ingestion.rs

@@ -171,7 +171,7 @@ impl IngestionService {
             width,
             height,
             fps,
-            probe_json: Some(probe_json_str),
+            probe_json: serde_json::from_str(&probe_json_str).ok(),
             storage: Default::default(),
             status: VideoStatus::Pending,
             processing_status: Some(serde_json::json!({"phase": "REGISTERED"})),