feat: Add decoupled pipeline schema with separate PostgreSQL namespace

- Create consolidated migration (005_create_pipeline_schema.sql) with
  'pipeline' schema for all classification tables
- Update pipeline repositories to use schema prefix (pipeline.*)
- Add run_migrations() method to DatabaseManager
- Add CLI tool for running versioned migrations

Tables created in pipeline schema:
- reviews_raw, reviews_enriched (Stage 1)
- review_spans (Stage 2)
- issues, issue_spans, issue_events (Stage 3)
- fact_timeseries (Stage 4)
- urt_domains, urt_categories (taxonomy lookup)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

core/database.py

@@ -182,6 +182,66 @@ class DatabaseManager:
 
             log.info("Database schema initialized")
 
+    async def run_migrations(self, migrations_dir: str = "migrations/versions"):
+        """
+        Run versioned migrations from SQL files.
+
+        Args:
+            migrations_dir: Path to directory containing .sql migration files.
+                           Files are run in sorted order.
+
+        Returns:
+            Number of migrations applied.
+        """
+        from pathlib import Path
+
+        migrations_path = Path(migrations_dir)
+        if not migrations_path.exists():
+            log.warning(f"Migrations directory not found: {migrations_dir}")
+            return 0
+
+        async with self.pool.acquire() as conn:
+            # Create migrations tracking table
+            await conn.execute("""
+                CREATE TABLE IF NOT EXISTS _migrations (
+                    id SERIAL PRIMARY KEY,
+                    filename VARCHAR(255) UNIQUE NOT NULL,
+                    applied_at TIMESTAMP WITH TIME ZONE DEFAULT NOW()
+                )
+            """)
+
+            # Get already applied migrations
+            applied = await conn.fetch("SELECT filename FROM _migrations")
+            applied_set = {r["filename"] for r in applied}
+
+            # Find and run pending migrations
+            migration_files = sorted(migrations_path.glob("*.sql"))
+            migrations_run = 0
+
+            for migration_file in migration_files:
+                filename = migration_file.name
+                if filename in applied_set:
+                    continue
+
+                log.info(f"Running migration: {filename}")
+
+                async with conn.transaction():
+                    try:
+                        sql = migration_file.read_text()
+                        await conn.execute(sql)
+                        await conn.execute(
+                            "INSERT INTO _migrations (filename) VALUES ($1)",
+                            filename,
+                        )
+                        migrations_run += 1
+                        log.info(f"Migration {filename} applied successfully")
+                    except Exception as e:
+                        log.error(f"Migration {filename} failed: {e}")
+                        raise
+
+            log.info(f"Ran {migrations_run} migrations")
+            return migrations_run
+
     # ==================== Job Operations ====================
 
     async def create_job(