feat(tui): add cards view, mode switching, promote picker, and card detail

Stream/cards toggle with 1/2 keys. Cards view with intent filtering
(tab cycles grab/read/fill/all), sort cycling (s key), pinned-first
ordering, and affordance badges. Promote picker (p key) with card type
selection and auto-detection from body content. Detail view renders
card_data per type: checklist steps, template slots, decision fields,
link URLs.

Extracts generateCardData to internal/carddata for reuse across cmd
and tui packages.

internal/carddata/carddata_test.go

@@ -0,0 +1,151 @@
+package carddata
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/lerko/nib/internal/db"
+)
+
+func TestGenerateCardData_Snippet(t *testing.T) {
+	data := GenerateCardData(db.CardSnippet, "some snippet")
+	if data == nil || *data != "{}" {
+		t.Errorf("snippet should produce {}, got %v", data)
+	}
+}
+
+func TestGenerateCardData_Template(t *testing.T) {
+	data := GenerateCardData(db.CardTemplate, "deploy ${host} to ${env}")
+	if data == nil {
+		t.Fatal("expected non-nil data")
+	}
+
+	var parsed struct {
+		Slots []struct {
+			Name    string `json:"name"`
+			Default string `json:"default"`
+		} `json:"slots"`
+	}
+	if err := json.Unmarshal([]byte(*data), &parsed); err != nil {
+		t.Fatal(err)
+	}
+	if len(parsed.Slots) != 2 {
+		t.Fatalf("expected 2 slots, got %d", len(parsed.Slots))
+	}
+	if parsed.Slots[0].Name != "host" {
+		t.Errorf("first slot: %q", parsed.Slots[0].Name)
+	}
+	if parsed.Slots[1].Name != "env" {
+		t.Errorf("second slot: %q", parsed.Slots[1].Name)
+	}
+}
+
+func TestGenerateCardData_TemplateDedupe(t *testing.T) {
+	data := GenerateCardData(db.CardTemplate, "${x} and ${x}")
+	var parsed struct {
+		Slots []struct {
+			Name string `json:"name"`
+		} `json:"slots"`
+	}
+	json.Unmarshal([]byte(*data), &parsed)
+	if len(parsed.Slots) != 1 {
+		t.Errorf("duplicate slots should be deduped, got %d", len(parsed.Slots))
+	}
+}
+
+func TestGenerateCardData_TemplateNoSlots(t *testing.T) {
+	data := GenerateCardData(db.CardTemplate, "no placeholders here")
+	var parsed struct {
+		Slots []struct {
+			Name string `json:"name"`
+		} `json:"slots"`
+	}
+	json.Unmarshal([]byte(*data), &parsed)
+	if len(parsed.Slots) != 0 {
+		t.Errorf("expected empty slots, got %d", len(parsed.Slots))
+	}
+}
+
+func TestGenerateCardData_Checklist(t *testing.T) {
+	body := "[ ] step one\n[x] step two\n[ ] step three"
+	data := GenerateCardData(db.CardChecklist, body)
+	if data == nil {
+		t.Fatal("expected non-nil data")
+	}
+
+	var parsed struct {
+		Steps []struct {
+			Text string `json:"text"`
+			Done bool   `json:"done"`
+		} `json:"steps"`
+	}
+	if err := json.Unmarshal([]byte(*data), &parsed); err != nil {
+		t.Fatal(err)
+	}
+	if len(parsed.Steps) != 3 {
+		t.Fatalf("expected 3 steps, got %d", len(parsed.Steps))
+	}
+	if parsed.Steps[0].Text != "step one" || parsed.Steps[0].Done {
+		t.Errorf("step 0: %+v", parsed.Steps[0])
+	}
+	if parsed.Steps[1].Text != "step two" || !parsed.Steps[1].Done {
+		t.Errorf("step 1: %+v", parsed.Steps[1])
+	}
+}
+
+func TestGenerateCardData_ChecklistFallback(t *testing.T) {
+	data := GenerateCardData(db.CardChecklist, "no checkbox syntax")
+	var parsed struct {
+		Steps []struct {
+			Text string `json:"text"`
+			Done bool   `json:"done"`
+		} `json:"steps"`
+	}
+	json.Unmarshal([]byte(*data), &parsed)
+	if len(parsed.Steps) != 1 {
+		t.Fatalf("fallback should produce 1 step, got %d", len(parsed.Steps))
+	}
+	if parsed.Steps[0].Text != "no checkbox syntax" {
+		t.Errorf("fallback step text: %q", parsed.Steps[0].Text)
+	}
+}
+
+func TestGenerateCardData_Decision(t *testing.T) {
+	data := GenerateCardData(db.CardDecision, "which db?")
+	var parsed struct {
+		Chose    string   `json:"chose"`
+		Why      string   `json:"why"`
+		Rejected []string `json:"rejected"`
+	}
+	if err := json.Unmarshal([]byte(*data), &parsed); err != nil {
+		t.Fatal(err)
+	}
+	if parsed.Chose != "" || parsed.Why != "" {
+		t.Error("decision fields should start empty")
+	}
+	if len(parsed.Rejected) != 0 {
+		t.Error("rejected should start empty")
+	}
+}
+
+func TestGenerateCardData_Link(t *testing.T) {
+	data := GenerateCardData(db.CardLink, "check https://example.com/path for details")
+	var parsed struct {
+		URL string `json:"url"`
+	}
+	json.Unmarshal([]byte(*data), &parsed)
+	if parsed.URL != "https://example.com/path" {
+		t.Errorf("url: %q", parsed.URL)
+	}
+}
+
+func TestGenerateCardData_LinkNoURL(t *testing.T) {
+	data := GenerateCardData(db.CardLink, "no url here")
+	var parsed struct {
+		URL string `json:"url"`
+	}
+	json.Unmarshal([]byte(*data), &parsed)
+	if parsed.URL != "" {
+		t.Errorf("expected empty url, got %q", parsed.URL)
+	}
+}