Add architecture package and application skeleton

docs/storage/01_schema.md

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+# Persistent Storage Schema Draft
+
+## Database Target
+
+- production: PostgreSQL
+- local development: SQLite
+
+## Tables
+
+### projects
+
+- `project_id` pk
+- `name`
+- `config_blob`
+- `created_at`
+- `updated_at`
+
+### conversations
+
+- `conversation_id` pk
+- `project_id`
+- `title`
+- `created_at`
+- `updated_at`
+
+### messages
+
+- `message_id` pk
+- `conversation_id`
+- `role`
+- `content`
+- `attachments_json`
+- `created_at`
+
+### tasks
+
+- `task_id` pk
+- `project_id`
+- `conversation_id`
+- `goal`
+- `inputs_json`
+- `status`
+- `requested_mode`
+- `effective_mode`
+- `current_node_id`
+- `result_summary_json`
+- `created_at`
+- `updated_at`
+
+### task_graphs
+
+- `task_id` pk
+- `graph_version`
+- `graph_metadata_json`
+- `created_at`
+
+### task_nodes
+
+- `node_id` pk
+- `task_id`
+- `node_type`
+- `status`
+- `input_json`
+- `output_json`
+- `dependencies_json`
+- `assigned_runner`
+- `attempts`
+- `retryable`
+- `timeout_ms`
+- `created_at`
+- `updated_at`
+
+### task_events
+
+- `event_id` pk
+- `task_id`
+- `conversation_id`
+- `node_id`
+- `event_type`
+- `correlation_id`
+- `causation_id`
+- `payload_json`
+- `occurred_at`
+
+### confirmations
+
+- `confirmation_id` pk
+- `task_id`
+- `node_id`
+- `status`
+- `scope`
+- `decision_json`
+- `preview_json`
+- `comment`
+- `created_at`
+- `resolved_at`
+
+### worker_sessions
+
+- `session_id` pk
+- `worker_id`
+- `name`
+- `machine`
+- `os`
+- `version`
+- `status`
+- `capabilities_json`
+- `last_heartbeat_at`
+- `current_task_id`
+- `connected_at`
+- `disconnected_at`
+
+### model_invocations
+
+- `invocation_id` pk
+- `task_id`
+- `node_id`
+- `slot`
+- `provider`
+- `model`
+- `status`
+- `request_json`
+- `response_json`
+- `usage_json`
+- `fallback_from_invocation_id`
+- `created_at`
+
+### tool_invocations
+
+- `invocation_id` pk
+- `task_id`
+- `node_id`
+- `source_type`
+- `source_id`
+- `tool_name`
+- `status`
+- `request_json`
+- `response_json`
+- `created_at`
+
+### artifacts
+
+- `artifact_id` pk
+- `task_id`
+- `node_id`
+- `artifact_type`
+- `storage_uri`
+- `metadata_json`
+- `created_at`
+
+## Required Indexes
+
+- `tasks(status, updated_at)`
+- `task_nodes(task_id, status)`
+- `task_events(task_id, occurred_at)`
+- `confirmations(status, created_at)`
+- `worker_sessions(status, last_heartbeat_at)`
+