Implement tasks 25, 26 + completion visibility setting

Task 25: Multiple dashboards — dashboards table + migration, /d/[slug]
route, root redirect, dashboard tabs in nav with create/rename/delete/
set-default. Task 26: Editable dashboard — react-grid-layout drag/resize
editor, widget picker modal with per-widget configurator auto-generated
from default config, save/reset server actions with Zod validation.

Completion visibility: server-side per-user setting (hours) replaces
localStorage timer; queries filter completed items by updatedAt cutoff;
Settings page dropdown persists preference via server action.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

drizzle/0011_completion_visibility.sql

@@ -0,0 +1 @@
+ALTER TABLE "users" ADD COLUMN "completion_visibility_hours" integer NOT NULL DEFAULT 24;

drizzle/0012_dashboards.sql

@@ -0,0 +1,28 @@
+CREATE TABLE "dashboards" (
+  "id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+  "user_id" uuid NOT NULL REFERENCES "users"("id") ON DELETE CASCADE,
+  "name" text NOT NULL,
+  "slug" text NOT NULL,
+  "is_default" boolean NOT NULL DEFAULT false,
+  "position" integer NOT NULL DEFAULT 0,
+  "layout" jsonb NOT NULL DEFAULT '{"version":1,"widgets":[]}',
+  "created_at" timestamp with time zone NOT NULL DEFAULT now(),
+  "updated_at" timestamp with time zone NOT NULL DEFAULT now()
+);
+
+CREATE UNIQUE INDEX "dashboards_user_slug_uq" ON "dashboards" ("user_id", "slug");
+
+-- Migrate each existing user's default_dashboard_layout into a "Home" dashboard.
+-- Idempotent: ON CONFLICT DO NOTHING.
+INSERT INTO "dashboards" ("user_id", "name", "slug", "is_default", "position", "layout")
+SELECT
+  "id",
+  'Home',
+  'home',
+  true,
+  0,
+  COALESCE("default_dashboard_layout", '{"version":1,"widgets":[]}')
+FROM "users"
+ON CONFLICT DO NOTHING;
+
+ALTER TABLE "users" DROP COLUMN IF EXISTS "default_dashboard_layout";