feat: add teams/groups with dashboard scoping

Schema:
- teams table (name unique, description)
- team_members table (team_id, user_id, unique constraint)
- team_id column on dashboards

API:
- GET/POST/PATCH/DELETE /teams
- POST /teams/:id/members (add user)
- DELETE /teams/:id/members/:userId (remove user)
- dashboards support team_id on create/update

Frontend:
- Teams tab in admin: CRUD + member management with add/remove
- Sidebar: dashboards filtered to user's teams
  (unassigned dashboards visible to all)
- Compact dashboard picker dropdown in sidebar

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

drizzle/migrations/0005_spotty_leader.sql

@@ -0,0 +1,19 @@
+CREATE TABLE "team_members" (
+	"id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+	"team_id" uuid NOT NULL,
+	"user_id" uuid NOT NULL,
+	CONSTRAINT "team_members_team_id_user_id_unique" UNIQUE("team_id","user_id")
+);
+--> statement-breakpoint
+CREATE TABLE "teams" (
+	"id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+	"name" text NOT NULL,
+	"description" text,
+	"created_at" timestamp with time zone DEFAULT now(),
+	CONSTRAINT "teams_name_unique" UNIQUE("name")
+);
+--> statement-breakpoint
+ALTER TABLE "dashboards" ADD COLUMN "team_id" uuid;--> statement-breakpoint
+ALTER TABLE "team_members" ADD CONSTRAINT "team_members_team_id_teams_id_fk" FOREIGN KEY ("team_id") REFERENCES "public"."teams"("id") ON DELETE cascade ON UPDATE no action;--> statement-breakpoint
+ALTER TABLE "team_members" ADD CONSTRAINT "team_members_user_id_users_id_fk" FOREIGN KEY ("user_id") REFERENCES "public"."users"("id") ON DELETE cascade ON UPDATE no action;--> statement-breakpoint
+ALTER TABLE "dashboards" ADD CONSTRAINT "dashboards_team_id_teams_id_fk" FOREIGN KEY ("team_id") REFERENCES "public"."teams"("id") ON DELETE set null ON UPDATE no action;