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.

sources/registry.go

@@ -15,9 +15,6 @@ import (
 type PollFactory func(cfg config.SourceConfig) (PollSource, error)
 type StreamFactory func(cfg config.SourceConfig) (StreamSource, error)
 
-// Factory is the legacy alias for poll source factories.
-type Factory = PollFactory
-
 type Registry struct {
 	byPollDriver   map[string]PollFactory
 	byStreamDriver map[string]StreamFactory
@@ -30,13 +27,6 @@ func NewRegistry() *Registry {
 	}
 }
 
-// Register associates a driver name (e.g. "openmeteo_observation") with a factory.
-//
-// The driver string is the "lookup key" used by config.sources[].driver.
-func (r *Registry) Register(driver string, f PollFactory) {
-	r.RegisterPoll(driver, f)
-}
-
 // RegisterPoll associates a driver name with a polling-source factory.
 func (r *Registry) RegisterPoll(driver string, f PollFactory) {
 	driver = strings.TrimSpace(driver)
@@ -75,11 +65,6 @@ func (r *Registry) RegisterStream(driver string, f StreamFactory) {
 	r.byStreamDriver[driver] = f
 }
 
-// Build constructs a polling source from a SourceConfig by looking up cfg.Driver.
-func (r *Registry) Build(cfg config.SourceConfig) (PollSource, error) {
-	return r.BuildPoll(cfg)
-}
-
 // BuildPoll constructs a polling source from a SourceConfig by looking up cfg.Driver.
 func (r *Registry) BuildPoll(cfg config.SourceConfig) (PollSource, error) {
 	driver := strings.TrimSpace(cfg.Driver)