refactor!: introduce generic processors registry and remove normalize registry adapter

- add new `processors` package with canonical `Processor` interface
- add `processors.Registry` with Register/Build/BuildChain factory model
- switch `pipeline.Pipeline` to `[]processors.Processor`
- replace `normalize.Registry` + registry adapter with direct `normalize.Processor`
- remove `normalize/registry.go`
- update root docs to position normalize as one optional processing stage
- add tests for processors registry, normalize processor behavior, and pipeline flow

BREAKING CHANGE:
- `pipeline.Processor` removed; use `processors.Processor`
- `normalize.Registry` and old normalize processor adapter APIs removed
- downstream daemons must update processor wiring to new `processors.Registry`
  and `normalize.NewProcessor(...)`

doc.go

@@ -5,16 +5,15 @@
 //
 // Conceptual flow:
 //
-//	Collect -> Normalize (optional) -> Policy -> Route -> Emit
+//	Collect -> Process (optional stages, including normalize) -> Route -> Emit
 //
 // In feedkit this maps to:
 //
-//	Collect:   sources + scheduler
-//	Normalize: normalize (optional pipeline stage)
-//	Policy:    pipeline
-//	Route:     dispatch
-//	Emit:      sinks
-//	Config:    config
+//	Collect: sources + scheduler
+//	Process: pipeline + processors + normalize (optional stage)
+//	Route:   dispatch
+//	Emit:    sinks
+//	Config:  config
 //
 // feedkit intentionally does not define domain payload schemas or domain-specific
 // validation rules. Those belong in each concrete daemon.
@@ -62,8 +61,11 @@
 //     Processor chain between scheduler and dispatch.
 //     Processors can transform, drop, or reject events.
 //
+//   - processors
+//     Generic processor interface and named factory registry for wiring chains.
+//
 //   - normalize
-//     Optional pipeline processor for raw->canonical mapping.
+//     Concrete pipeline processor for raw->canonical mapping.
 //     If no normalizer matches, the event passes through unchanged by default.
 //
 //   - dispatch