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.

transport/http.go

@@ -10,10 +10,10 @@ import (
 	"time"
 )
 
-// maxResponseBodyBytes is a hard safety limit on HTTP response bodies.
+// DefaultHTTPResponseBodyLimitBytes is a hard safety limit on HTTP response bodies.
 // API responses should be small, so this protects us from accidental
 // or malicious large responses.
-const maxResponseBodyBytes = 2 << 21 // 4 MiB
+const DefaultHTTPResponseBodyLimitBytes int64 = 2 << 21 // 4 MiB
 
 // DefaultHTTPTimeout is the standard timeout used by HTTP sources.
 // Individual drivers may override this if they have a specific need.
@@ -29,6 +29,10 @@ func NewHTTPClient(timeout time.Duration) *http.Client {
 }
 
 func FetchBody(ctx context.Context, client *http.Client, url, userAgent, accept string) ([]byte, error) {
+	return FetchBodyWithLimit(ctx, client, url, userAgent, accept, DefaultHTTPResponseBodyLimitBytes)
+}
+
+func FetchBodyWithLimit(ctx context.Context, client *http.Client, url, userAgent, accept string, bodyLimitBytes int64) ([]byte, error) {
 	res, err := doRequest(ctx, client, http.MethodGet, url, userAgent, accept, "", "")
 	if err != nil {
 		return nil, err
@@ -39,7 +43,7 @@ func FetchBody(ctx context.Context, client *http.Client, url, userAgent, accept
 		return nil, fmt.Errorf("HTTP %s", res.Status)
 	}
 
-	return readValidatedBody(res.Body)
+	return readValidatedBody(res.Body, bodyLimitBytes)
 }
 
 // HTTPValidators are cache validators learned from prior successful GET responses.
@@ -68,6 +72,17 @@ func FetchBodyIfChanged(
 	url, userAgent, accept string,
 	conditional bool,
 	validators HTTPValidators,
+) ([]byte, bool, HTTPValidators, error) {
+	return FetchBodyIfChangedWithLimit(ctx, client, url, userAgent, accept, conditional, validators, DefaultHTTPResponseBodyLimitBytes)
+}
+
+func FetchBodyIfChangedWithLimit(
+	ctx context.Context,
+	client *http.Client,
+	url, userAgent, accept string,
+	conditional bool,
+	validators HTTPValidators,
+	bodyLimitBytes int64,
 ) ([]byte, bool, HTTPValidators, error) {
 	headerName, headerValue := conditionalHeader(conditional, validators)
 
@@ -89,7 +104,7 @@ func FetchBodyIfChanged(
 		}
 	}
 
-	b, err := readValidatedBody(res.Body)
+	b, err := readValidatedBody(res.Body, bodyLimitBytes)
 	if err != nil {
 		return nil, false, validators, err
 	}
@@ -150,9 +165,13 @@ func refreshValidators(current HTTPValidators, header http.Header) HTTPValidator
 	return current
 }
 
-func readValidatedBody(r io.Reader) ([]byte, error) {
-	// Read at most maxResponseBodyBytes + 1 so we can detect overflow.
-	limited := io.LimitReader(r, maxResponseBodyBytes+1)
+func readValidatedBody(r io.Reader, bodyLimitBytes int64) ([]byte, error) {
+	if bodyLimitBytes <= 0 {
+		bodyLimitBytes = DefaultHTTPResponseBodyLimitBytes
+	}
+
+	// Read at most bodyLimitBytes + 1 so we can detect overflow.
+	limited := io.LimitReader(r, bodyLimitBytes+1)
 
 	b, err := io.ReadAll(limited)
 	if err != nil {
@@ -163,8 +182,8 @@ func readValidatedBody(r io.Reader) ([]byte, error) {
 		return nil, fmt.Errorf("empty response body")
 	}
 
-	if len(b) > maxResponseBodyBytes {
-		return nil, fmt.Errorf("response body too large (>%d bytes)", maxResponseBodyBytes)
+	if int64(len(b)) > bodyLimitBytes {
+		return nil, fmt.Errorf("response body too large (>%d bytes)", bodyLimitBytes)
 	}
 
 	return b, nil