feat: worker plugin system — domain ports, pipeline executor, built-in plugins

- PluginExecutor + PluginRegistry ports in domain
- ExecutePipelineCommand orchestrates job→pipeline→plugin steps
- ProcessNextJobCommand polls + executes next queued job
- InMemoryPluginRegistry, NoOp/MetadataExtractor/SidecarSync plugins
- Worker main rewritten with poll loop, factories module for DI
- Deleted template job/runner/jobs remnants

crates/worker/Cargo.toml

@@ -8,10 +8,11 @@ name = "k_photos-worker"
 path = "src/main.rs"
 
 [dependencies]
-domain     = { workspace = true }
-
+domain            = { workspace = true }
+application       = { workspace = true }
 
 adapters-postgres = { path = "../adapters/postgres" }
+adapters-storage  = { workspace = true }
 
 tokio             = { workspace = true }
 anyhow            = { workspace = true }