feat(atlas): surface the user's own Gitea repos on stage 05 (#10)

Adds the repos panel from #4's "Not yet shipped" list, following the shipped
issues slice (b2761a4) structurally rather than inventing a second approach:

- internal/atlas/repos.go — RepoNodes(), a pure parser over an already-decoded
  /user/repos response. Archived repos are dropped: the atlas shows where work
  happens, and an archived repo is by definition somewhere it does not.
- internal/gitea/client.go — MyRepos(), same PAT and same contract as MyIssues:
  errors when GITEA_TOKEN is unset so the caller skips the overlay rather than
  issuing an unauthenticated request. That unset path is the one running in
  prod today (#4), so it is tested, not assumed.
- internal/web/handler.go — wired into liveOverlay().

Stage 05 is the right home — repos are what the execution stage acts on — but
#11 had just claimed its `generate` key for stuck-badges, and a stage could
only name one source. So `generate` now accepts either spelling:

    "generate": "ci-jobs"
    "generate": ["stuck-badges", "gitea-repos"]

The bare string stays valid and marshals back as a bare string, so no authored
stage is rewritten and the frontend contract is unchanged. Stages 04 and 08
already share stuck-badges between them; this is the same growth one level in.

The overlay merge also moves out of the handler into atlas.PrependGenerated,
which is unit-testable where the inline loop was not — it sat behind a network
call. It covers the issues path too, and fixes a latent aliasing bug there: the
old `append(liveNodes, authored...)` wrote into the live slice's backing array,
so two stages sharing a key would corrupt each other. That shape is no longer
hypothetical now that stuck-badges spans three stages.

Verified end-to-end both ways: without GITEA_TOKEN the atlas returns 200 with
stage 05's authored nodes intact; with a real token stage 05 serves both
overlays at once — stuck badges, then eight live repos, then the authored
nodes — and a repo with no language emits one tag rather than an empty pill.

task check green (golangci-lint 0 issues, vet, -race).

Closes #10.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/atlas/generate_test.go

@@ -0,0 +1,66 @@
+package atlas_test
+
+import (
+	"encoding/json"
+	"testing"
+
+	"git.d-ma.be/mathias/cad-atlas/internal/atlas"
+)
+
+// Every stage authored before this type existed spells `generate` as a bare
+// string. That spelling stays valid — this is additive, not a migration.
+func TestGenerateKeys_UnmarshalsBareString(t *testing.T) {
+	var s atlas.Stage
+	if err := json.Unmarshal([]byte(`{"no":"06","generate":"ci-jobs"}`), &s); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if !s.Generate.Has("ci-jobs") {
+		t.Fatalf("Has(ci-jobs) false for %+v", s.Generate)
+	}
+	if s.Generate.Has("gitea-repos") {
+		t.Fatal("Has matched a key that is not present")
+	}
+}
+
+func TestGenerateKeys_UnmarshalsList(t *testing.T) {
+	var s atlas.Stage
+	if err := json.Unmarshal([]byte(`{"no":"05","generate":["stuck-badges","gitea-repos"]}`), &s); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if !s.Generate.Has("stuck-badges") || !s.Generate.Has("gitea-repos") {
+		t.Fatalf("both keys should match, got %+v", s.Generate)
+	}
+}
+
+func TestGenerateKeys_AbsentMatchesNothing(t *testing.T) {
+	var s atlas.Stage
+	if err := json.Unmarshal([]byte(`{"no":"00"}`), &s); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if s.Generate.Has("") || s.Generate.Has("ci-jobs") {
+		t.Fatalf("absent generate matched something: %+v", s.Generate)
+	}
+}
+
+// The frontend reads this JSON, so the round-trip must stay stable.
+func TestGenerateKeys_RoundTrips(t *testing.T) {
+	for _, raw := range []string{`{"generate":"ci-jobs"}`, `{"generate":["a","b"]}`} {
+		var s atlas.Stage
+		if err := json.Unmarshal([]byte(raw), &s); err != nil {
+			t.Fatalf("unmarshal %s: %v", raw, err)
+		}
+		out, err := json.Marshal(s)
+		if err != nil {
+			t.Fatalf("marshal: %v", err)
+		}
+		var back atlas.Stage
+		if err := json.Unmarshal(out, &back); err != nil {
+			t.Fatalf("re-unmarshal %s: %v", out, err)
+		}
+		for _, k := range []string{"ci-jobs", "a", "b"} {
+			if s.Generate.Has(k) != back.Generate.Has(k) {
+				t.Fatalf("round-trip lost %q: %s -> %s", k, raw, out)
+			}
+		}
+	}
+}