feat(gitea): surface mathias's own open Gitea issues on stage 03 (#4)

TDD: IssueNodes parses /repos/issues/search into stage nodes (title, repo
tag, clickable html_url). gitea.MyIssues() reads GITEA_TOKEN and skips
gracefully when unset, mirroring the existing liveOverlay fallback pattern.

Single-operator homelab, not per-visitor OAuth: a static read-only PAT
gates on "cleared Authentik forward-auth", not per-user token exchange —
see #4 discussion. GITEA_TOKEN provisioning in infra (ExternalSecret) is
a separate follow-up; without it the overlay is inert (no crash, just no
live nodes), so this ships safely ahead of that wiring.

Nodes with a url now render as clickable <a class="node"> instead of
<div class="node">.

internal/atlas/issues_test.go

@@ -0,0 +1,41 @@
+package atlas_test
+
+import (
+	"testing"
+
+	"git.d-ma.be/mathias/cad-atlas/internal/atlas"
+)
+
+func TestIssueNodes_OneNodePerIssueWithRepoTagAndURL(t *testing.T) {
+	search := []byte(`[
+	  {"number":212,"title":"segment-embedder: add smoke test","html_url":"https://git.d-ma.be/mathias/infra/issues/212","repository":{"full_name":"mathias/infra"}},
+	  {"number":8,"title":"Write cad-atlas's own vargo-gate candidate","html_url":"https://git.d-ma.be/mathias/cad-atlas/issues/8","repository":{"full_name":"mathias/cad-atlas"}}
+	]`)
+
+	nodes, err := atlas.IssueNodes(search)
+	if err != nil {
+		t.Fatalf("IssueNodes: %v", err)
+	}
+	if len(nodes) != 2 {
+		t.Fatalf("want 2 nodes, got %d", len(nodes))
+	}
+	if nodes[0].Title != "#212 segment-embedder: add smoke test" {
+		t.Fatalf("title = %q", nodes[0].Title)
+	}
+	if nodes[0].URL != "https://git.d-ma.be/mathias/infra/issues/212" {
+		t.Fatalf("url = %q", nodes[0].URL)
+	}
+	if len(nodes[0].Tags) != 2 || nodes[0].Tags[0] != "live · Gitea" || nodes[0].Tags[1] != "mathias/infra" {
+		t.Fatalf("tags = %v", nodes[0].Tags)
+	}
+}
+
+func TestIssueNodes_EmptyListReturnsEmptyNotNil(t *testing.T) {
+	nodes, err := atlas.IssueNodes([]byte(`[]`))
+	if err != nil {
+		t.Fatalf("IssueNodes: %v", err)
+	}
+	if nodes == nil || len(nodes) != 0 {
+		t.Fatalf("nodes = %+v, want empty non-nil slice", nodes)
+	}
+}