storage: retire legacy execution writer exports

[likun666661]

Part of #1649.

Summary

• remove the retired AgentRun, RuntimeEvent, and ShellRun file-writer constructors from the production @maka/storage entrypoint
• isolate legacy writer construction behind an explicitly named test-support subpath for import and compatibility fixtures
• expose RuntimeEvent compatibility readers through a frozen read-only facade for both legacy JSONL and SQLite
• update cross-package compatibility tests to use the explicit legacy fixture boundary

Invariants

• production imports cannot obtain createAgentRunStore, createRuntimeEventStore, or createShellRunStore from @maka/storage
• legacy codecs and file implementations remain internal so existing state can still be imported and compatibility-tested
• RuntimeEvent readers do not expose appendRuntimeEvent, even when backed by a read-only SQLite connection
• no production source imports the legacy test-support subpath

Verification

• npm run build:test
• npm run typecheck
• npm run lint
• npm run format:check
• full @maka/storage test suite
• 84/84 affected @maka/runtime tests with test concurrency 1
• 5/5 affected @maka/headless tests with test concurrency 1
• focused CLI, Desktop, Runtime Host, RuntimeEvent transfer, and public-surface tests