feat: frame/time pipeline split + output validation

- Add PipelineType enum + pipeline() to ProcessorType
- Split ProcessorPool into frame_slots (max 2) and time_slots (max 1)
- Add can_start_for() for pipeline-aware scheduling
- Add validate_output_file() — checks JSON validity before marking complete
- Add 3 unit tests for validate_output_file()
- Create DESIGN/FRAME_TIME_PIPELINE_V1.0.md (492 lines)

src/core/db/mod.rs

@@ -43,7 +43,7 @@ pub use mongodb_db::MongoDb;
 pub use postgres_db::{
     Bm25Result, CandidateRecord, CreateApiKeyConfig, FileIdentityRecord, FileRecord,
     HybridSearchResult, IdentityChunkRecord, IdentityDetailRecord, IdentityFaceRecord,
-    IdentityFileRecord, MonitorJob, MonitorJobStats, MonitorJobStatus, PostgresDb,
+    IdentityFileRecord, MonitorJob, MonitorJobStats, MonitorJobStatus, PipelineType, PostgresDb,
     ProcessorJobStatus, ProcessorResult, ProcessorType, ResourceRecord, VideoRecord, VideoStatus,
 };
 pub use qdrant_db::{QdrantDb, VectorPayload};