feat(HAI-113): add structured logger and replace console calls

- Create logger module with log levels and structured output (packages/engine/src/logger.ts)
- Replace console.log/warn/error calls with structured logger across engine modules
- Export logger from engine package index
- Add comprehensive tests for logger functionality
- Clean up CI/release workflows and update docs

packages/engine/src/index.ts

@@ -7,3 +7,4 @@ export { aiMergeTask, type MergerOptions } from "./merger.js";
 export { reviewStep, type ReviewType, type ReviewVerdict, type ReviewResult, type ReviewOptions } from "./reviewer.js";
 export { createHaiAgent, type AgentOptions, type AgentResult } from "./pi.js";
 export { WorktreePool } from "./worktree-pool.js";
+export { createLogger, type Logger } from "./logger.js";