Implement linear task chains and recurring maintenance buckets

Backend, web timeline, and Android widget wiring for the last two
unimplemented items from doot-future-task-scheduling-ideas.

Chains: task_chains table + chain_id/chain_position/chain_unlocked on
native_tasks (migration 026), WIP-limit-1 advancement hooked into
CompleteNativeTask, locked tasks excluded from all date-based queries,
5 new /api/widget/chains* endpoints, an N/M position badge on web and
Android widget rows.

Buckets: maintenance_buckets table + bucket_id/bucket_state/
bucket_last_active_at on native_tasks (migration 027),
staleness-then-priority selection scoring, a new RunBucketCycleCheck
scheduler loop, 5 new endpoints including the distinct Defer action, a
Defer button on web and Android widget rows.

Also corrected stale "not yet approved" status headers on the two
already-shipped specs this work depended on (labels/projects, budgets/
availability) -- their headers were never updated after implementation.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EZ7ikw2ukGJFTHE3bJS7zL

1 files changed, 43 insertions, 0 deletions

diff --git a/internal/handlers/chains_timeline_test.go b/internal/handlers/chains_timeline_test.go
new file mode 100644
index 0000000..76ceb68
--- /dev/null
+++ b/internal/handlers/chains_timeline_test.go
@@ -0,0 +1,43 @@
+package handlers
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+func TestBuildTimeline_PopulatesChainBadgeForUnlockedTask(t *testing.T) {
+	s, cleanup := setupTestDB(t)
+	defer cleanup()
+
+	chain, err := s.CreateChain("Ham Radio Track", []string{"Study Technician", "Pass exam", "Study General"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	tasks, err := s.GetChainTasks(chain.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	now := time.Now()
+	items, err := BuildTimeline(context.Background(), s, now.Add(-time.Hour), now.Add(24*time.Hour))
+	if err != nil {
+		t.Fatalf("BuildTimeline: %v", err)
+	}
+
+	var found bool
+	for _, item := range items {
+		if item.ID == tasks[0].ID {
+			found = true
+			if item.ChainPosition != 1 || item.ChainTotal != 3 {
+				t.Errorf("ChainPosition/ChainTotal = %d/%d, want 1/3", item.ChainPosition, item.ChainTotal)
+			}
+		}
+		if item.ID == tasks[1].ID || item.ID == tasks[2].ID {
+			t.Errorf("locked chain task %q should not appear in the timeline", item.ID)
+		}
+	}
+	if !found {
+		t.Fatal("expected the unlocked chain task (position 0) to appear in the timeline")
+	}
+}