fix: wire handler layer in main.go and fix migration issues

cmd/server/main.go: replace stub router with full wiring —
  UserRepo, SessionRepo, AuthService, AuthMiddleware, AuthHandler,
  NewRouter; use postgres.NewPool instead of pgxpool.New directly.

migrations/001_init_schemas.sql: wrap uuid_v7 and uuid_extract_timestamp
  function bodies with goose StatementBegin/End so semicolons inside
  dollar-quoted strings are not treated as statement separators.

migrations/007_seed_data.sql: add seed admin user (admin/admin,
  bcrypt cost 10, is_admin=true, can_create=true) for manual testing.

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

backend/migrations/001_init_schemas.sql

@@ -9,6 +9,7 @@ CREATE SCHEMA IF NOT EXISTS acl;
 CREATE SCHEMA IF NOT EXISTS activity;
 
 -- UUID v7 generator
+-- +goose StatementBegin
 CREATE OR REPLACE FUNCTION public.uuid_v7(cts timestamptz DEFAULT clock_timestamp())
 RETURNS uuid LANGUAGE plpgsql AS $$
 DECLARE
@@ -38,14 +39,17 @@ BEGIN
             substring(entropy from 1 for 12))::uuid;
 END;
 $$;
+-- +goose StatementEnd
 
 -- Extract timestamp from UUID v7
+-- +goose StatementBegin
 CREATE OR REPLACE FUNCTION public.uuid_extract_timestamp(uuid_val uuid)
 RETURNS timestamptz LANGUAGE sql IMMUTABLE PARALLEL SAFE AS $$
     SELECT to_timestamp(
         ('x' || left(replace(uuid_val::text, '-', ''), 12))::bit(48)::bigint / 1000.0
     );
 $$;
+-- +goose StatementEnd
 
 -- +goose Down