refactor(schema): decode effect schemas directly

[kitlangton]

Summary

• Replace Effect-derived .zod.parse calls with cached Schema.decodeUnknownSync decoders.
• Decode ACP todo JSON with Schema.fromJsonString(Schema.Array(Todo.Info)) instead of JSON.parse plus Zod safeParse.
• Decode PTY IDs with the Effect schema at the websocket boundary.

Testing

• bun typecheck from packages/opencode
• bun run test:ci test/cli/import.test.ts from packages/opencode
• bun run test:ci test/project/worktree.test.ts test/project/worktree-remove.test.ts from packages/opencode
• bun run test:ci test/pty/pty-session.test.ts from packages/opencode
• push hook bun turbo typecheck