Add admin users, BYOC teams, hosts schema, and Redis for host registration

Introduce three migrations: admin permissions (is_admin + permissions table),
BYOC team tracking, and multi-host support (hosts, host_tokens, host_tags).
Add Redis to dev infra and wire up client in control plane for ephemeral
host registration tokens. Add go-redis dependency.

db/migrations/20260316203135_admin_users.sql

@@ -0,0 +1,21 @@
+-- +goose Up
+
+ALTER TABLE users
+    ADD COLUMN is_admin BOOLEAN NOT NULL DEFAULT FALSE;
+
+CREATE TABLE admin_permissions (
+    id         TEXT PRIMARY KEY,
+    user_id    TEXT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    permission TEXT NOT NULL,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    UNIQUE (user_id, permission)
+);
+
+CREATE INDEX idx_admin_permissions_user ON admin_permissions(user_id);
+
+-- +goose Down
+
+DROP TABLE admin_permissions;
+
+ALTER TABLE users
+    DROP COLUMN is_admin;