fix: prevent false link-check failures and harden health/workflow errors

Address three review findings from the Go rewrite:\n\n- checker: update PartitionLinks to only classify HTTP(S) URLs as external links.\n  This skips markdown-relative targets (for example  and anchors) so\n  non-URL entries are no longer sent to HTTP validation and do not produce\n  deterministic "unsupported protocol scheme" failures.\n\n- health command: stop ignoring LoadHealthCache errors.\n  Return a user-facing "load cache" error when the cache file is unreadable\n  or invalid instead of allowing a nil cache panic on Merge.\n\n- broken links workflow: remove masked execution behavior from the link check\n  step. Capture awesome-docker check exit code, set has_errors=true on any\n  non-zero exit, and expose the exit code in the generated issue body so\n  checker failures are visible and cannot incorrectly close the tracking issue.\n\nTest coverage updates:\n- extend checker partition test to include markdown-relative/anchor targets\n  and verify they are not treated as external URLs.\n- add cache test for invalid YAML load failure.

internal/checker/github.go

@@ -3,6 +3,7 @@ package checker
 import (
 	"context"
 	"fmt"
+	"net/url"
 	"strings"
 	"time"
 
@@ -43,12 +44,20 @@ func ExtractGitHubRepo(url string) (owner, name string, ok bool) {
 	return parts[0], parts[1], true
 }
 
-// PartitionLinks separates URLs into GitHub repos and external links.
+func isHTTPURL(raw string) bool {
+	u, err := url.Parse(raw)
+	if err != nil {
+		return false
+	}
+	return u.Scheme == "http" || u.Scheme == "https"
+}
+
+// PartitionLinks separates URLs into GitHub repos and external HTTP(S) links.
 func PartitionLinks(urls []string) (github, external []string) {
 	for _, url := range urls {
 		if _, _, ok := ExtractGitHubRepo(url); ok {
 			github = append(github, url)
-		} else {
+		} else if isHTTPURL(url) {
 			external = append(external, url)
 		}
 	}