fix: replace conflicting migration 003 with no-op

Migration 003 tried to recreate tables (users, channel_members, messages)
with INTEGER IDs, conflicting with 002_schema.sql which already defines
them with TEXT UUIDs. This caused all tests to fail.

internal/db/schema/003_users.sql

@@ -1,31 +1,4 @@
-PRAGMA foreign_keys = ON;
-
-CREATE TABLE IF NOT EXISTS users (
-    id INTEGER PRIMARY KEY AUTOINCREMENT,
-    nick TEXT NOT NULL UNIQUE,
-    token TEXT NOT NULL UNIQUE,
-    created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
-    last_seen DATETIME DEFAULT CURRENT_TIMESTAMP
-);
-
-CREATE TABLE IF NOT EXISTS channel_members (
-    id INTEGER PRIMARY KEY AUTOINCREMENT,
-    channel_id INTEGER NOT NULL REFERENCES channels(id) ON DELETE CASCADE,
-    user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
-    joined_at DATETIME DEFAULT CURRENT_TIMESTAMP,
-    UNIQUE(channel_id, user_id)
-);
-
-CREATE TABLE IF NOT EXISTS messages (
-    id INTEGER PRIMARY KEY AUTOINCREMENT,
-    channel_id INTEGER REFERENCES channels(id) ON DELETE CASCADE,
-    user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
-    content TEXT NOT NULL,
-    is_dm INTEGER NOT NULL DEFAULT 0,
-    dm_target_id INTEGER REFERENCES users(id) ON DELETE CASCADE,
-    created_at DATETIME DEFAULT CURRENT_TIMESTAMP
-);
-
-CREATE INDEX IF NOT EXISTS idx_messages_channel ON messages(channel_id, created_at);
-CREATE INDEX IF NOT EXISTS idx_messages_dm ON messages(user_id, dm_target_id, created_at);
-CREATE INDEX IF NOT EXISTS idx_users_token ON users(token);
+-- Migration 003: no-op (schema already created by 002_schema.sql)
+-- This migration previously conflicted with 002 by attempting to recreate
+-- tables with incompatible column types (INTEGER vs TEXT IDs).
+SELECT 1;