Refactor feedkit boundaries ahead of v1

Remove global Postgres schema registration in favor of explicit schema-aware sink factory wiring, and update weatherfeeder to register the Postgres sink explicitly. Add optional per-source HTTP timeout and response body limit overrides while keeping feedkit defaults. Remove remaining legacy source/config compatibility surfaces, including singular kind support and old source registry/type aliases, and migrate weatherfeeder sources to plural `Kinds()` metadata. Clean up related docs, tests, and sample config to match the new Postgres, HTTP, and NATS configuration model.

sinks/postgres_schema.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"fmt"
 	"strings"
-	"sync"
 	"time"
 
 	"gitea.maximumdirect.net/ejr/feedkit/event"
@@ -72,51 +71,6 @@ type postgresTableCompiled struct {
 	indexes     []PostgresIndex
 }
 
-var (
-	postgresSchemaRegistryMu sync.RWMutex
-	postgresSchemaRegistry   = map[string]postgresSchemaCompiled{}
-)
-
-// RegisterPostgresSchema registers one downstream schema by sink name.
-//
-// This should be called by downstream daemon wiring code before sink
-// construction. Duplicate sink-name registrations are rejected.
-func RegisterPostgresSchema(sinkName string, schema PostgresSchema) error {
-	sinkName = strings.TrimSpace(sinkName)
-	if sinkName == "" {
-		return fmt.Errorf("postgres schema: sink name cannot be empty")
-	}
-
-	compiled, err := compilePostgresSchema(schema)
-	if err != nil {
-		return err
-	}
-
-	postgresSchemaRegistryMu.Lock()
-	defer postgresSchemaRegistryMu.Unlock()
-
-	if _, exists := postgresSchemaRegistry[sinkName]; exists {
-		return fmt.Errorf("postgres schema: sink %q already registered", sinkName)
-	}
-
-	postgresSchemaRegistry[sinkName] = compiled
-	return nil
-}
-
-func MustRegisterPostgresSchema(sinkName string, schema PostgresSchema) {
-	if err := RegisterPostgresSchema(sinkName, schema); err != nil {
-		panic(err)
-	}
-}
-
-func lookupPostgresSchema(sinkName string) (postgresSchemaCompiled, bool) {
-	postgresSchemaRegistryMu.RLock()
-	defer postgresSchemaRegistryMu.RUnlock()
-
-	s, ok := postgresSchemaRegistry[sinkName]
-	return s, ok
-}
-
 func compilePostgresSchema(schema PostgresSchema) (postgresSchemaCompiled, error) {
 	if schema.MapEvent == nil {
 		return postgresSchemaCompiled{}, fmt.Errorf("postgres schema: map function is required")