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/model.go

@@ -32,16 +32,16 @@ type Node struct {
 // moves work forward and what must be true to advance. When Generate is set,
 // Nodes are derived from a live source at Build time.
 type Stage struct {
-	No         string `json:"no"`
-	Short      string `json:"short,omitempty"`
-	Title      string `json:"title"`
-	PlainTitle string `json:"plain_title,omitempty"`
-	Plain      string `json:"plain,omitempty"`
-	Path       string `json:"path,omitempty"`
-	Cls        string `json:"cls,omitempty"`
-	Generate   string `json:"generate,omitempty"`
-	TransLabel string `json:"trans_label,omitempty"`
-	Trans      string `json:"trans,omitempty"`
+	No         string       `json:"no"`
+	Short      string       `json:"short,omitempty"`
+	Title      string       `json:"title"`
+	PlainTitle string       `json:"plain_title,omitempty"`
+	Plain      string       `json:"plain,omitempty"`
+	Path       string       `json:"path,omitempty"`
+	Cls        string       `json:"cls,omitempty"`
+	Generate   GenerateKeys `json:"generate,omitempty"`
+	TransLabel string       `json:"trans_label,omitempty"`
+	Trans      string       `json:"trans,omitempty"`
 	// StuckCount/AwaitingCount are set by ApplyStuckOverlay (cad-atlas#11) on
 	// stages marked `"generate":"stuck-badges"` — the two visual classes the
 	// issue asks for kept as separate counts so a functioning control
@@ -71,7 +71,7 @@ func Build(atlasJSON, workflow []byte) (Atlas, error) {
 		return Atlas{}, fmt.Errorf("parse atlas data: %w", err)
 	}
 	for i := range a.Stages {
-		if a.Stages[i].Generate != "ci-jobs" {
+		if !a.Stages[i].Generate.Has("ci-jobs") {
 			continue
 		}
 		jobs, err := JobsFromWorkflow(workflow)