Add architecture package and application skeleton

docs/architecture/05_state_machines.md

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+# State Machines
+
+## TaskStatus
+
+```text
+created
+  -> planned
+  -> running
+  -> waiting_confirmation
+  -> waiting_manual
+  -> completed
+  -> failed
+  -> cancelled
+```
+
+Правила:
+
+- `created -> planned`: planner graph создан;
+- `planned -> running`: есть готовые к исполнению nodes;
+- `running -> waiting_confirmation`: execution остановлен на pending approval;
+- `running -> waiting_manual`: policy/manual gate остановил автостарт;
+- `running -> completed`: finalizer сформировал итог;
+- `running -> failed`: unrecoverable error;
+- `waiting_confirmation -> running`: approval получен;
+- `waiting_manual -> running`: пользователь вручную продолжил выполнение.
+
+## NodeStatus
+
+```text
+pending
+  -> ready
+  -> running
+  -> waiting_confirmation
+  -> completed
+  -> failed
+  -> skipped
+  -> cancelled
+```
+
+## ConfirmationStatus
+
+```text
+pending
+  -> approved
+  -> rejected
+  -> expired
+  -> cancelled
+```
+
+## WorkerSessionStatus
+
+```text
+connecting
+  -> online
+  -> busy
+  -> stale
+  -> disconnected
+```
+
+## Retry Principles
+
+- retry выполняется только для явно retryable failures;
+- retry history фиксируется в node attempts и event log;
+- confirmation-required state не считается failure;
+- idempotency must be explicit for side-effecting nodes.
+