Implement sales CRM workflow foundation

migrations/sql/0027_sales_automation_task_locks_sqlite.sql

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+ALTER TABLE sales_automation_tasks ADD COLUMN locked_at TEXT;
+ALTER TABLE sales_automation_tasks ADD COLUMN locked_by TEXT;
+ALTER TABLE sales_automation_tasks ADD COLUMN completed_at TEXT;
+ALTER TABLE sales_automation_tasks ADD COLUMN failed_at TEXT;
+ALTER TABLE sales_automation_tasks ADD COLUMN max_retries INTEGER NOT NULL DEFAULT 3;
+
+CREATE INDEX IF NOT EXISTS idx_sales_tasks_lock ON sales_automation_tasks(status, locked_at, locked_by);