feat: implement profile summary cards with GraphQL fetch and Action wrapper

- Add GraphQL client fetching profile, stats, language aggregation, and
  per-repo commit histograms for the productive-time heatmap.
- Render real SVG cards (profile details, top languages, stats grid,
  weekday×hour heatmap) with XML escaping and thousands-formatted numbers.
- Expand theme palette to 30 built-ins ported from github-readme-stats;
  add -list-themes, multi-theme rendering, and 'all' shortcut.
- Package as Docker-based GitHub Action (action.yml, Dockerfile,
  entrypoint.sh) with optional auto-commit of generated cards.
- Release workflow publishes GHCR image and cross-platform binaries on
  v* tags.
- Unit tests cover rendering, XML escape, number formatting, language sort.

internal/github/profile_test.go

@@ -0,0 +1,34 @@
+package github
+
+import "testing"
+
+func TestSortLanguages(t *testing.T) {
+	bytes := map[string]int64{
+		"Go":         500,
+		"Python":     300,
+		"TypeScript": 500, // tie with Go → alphabetical wins
+		"HTML":       100,
+	}
+	colors := map[string]string{
+		"Go":         "#00ADD8",
+		"Python":     "#3572A5",
+		"TypeScript": "#3178c6",
+	}
+	got := sortLanguages(bytes, colors)
+
+	wantOrder := []string{"Go", "TypeScript", "Python", "HTML"}
+	if len(got) != len(wantOrder) {
+		t.Fatalf("len=%d want %d", len(got), len(wantOrder))
+	}
+	for i, name := range wantOrder {
+		if got[i].Name != name {
+			t.Errorf("pos %d: %q want %q", i, got[i].Name, name)
+		}
+	}
+	if got[0].Color != "#00ADD8" {
+		t.Errorf("Go color=%q want #00ADD8", got[0].Color)
+	}
+	if got[3].Color != "" {
+		t.Errorf("HTML color=%q want empty (missing from colors)", got[3].Color)
+	}
+}