#11305: fix(logging): remove redundant subsystem prefix from log output

## Summary Removes duplicate subsystem display in `openclaw logs` output by eliminating tslog's `prefix` option from `getChildLogger()`. ## Problem Each log line showed the subsystem twice: ``` 17:20:00 info gateway/channels/feishu {"subsystem":"gateway/channels/feishu"} feishu[default]: received message... ``` The first occurrence is the label (correctly extracted from `_meta.name`). The second is redundant noise from tslog's prefix mechanism leaking into positional args. ## Root Cause The `prefix` was added during the pino → tslog migration (commit `d463c82c9`) as an attempt to preserve pino's child logger binding behavior. However: - `name` already captures the subsystem in `_meta.name` - `parseLogLine` extracts subsystem from `_meta.name` - `prefix` just injects redundant subsystem JSON into message body ## Changes 1. **src/logging/logger.ts** — Remove `prefix` from `getChildLogger()` options 2. **src/logging/parse-log-line.test.ts** — Update test to match new log format (no prefix in positional args) ## Result ``` 17:20:00 info gateway/channels/feishu feishu[default]: received message... ``` Clean, readable logs with no duplication. ## Test Plan - ✅ Unit tests pass: `pnpm test src/logging/parse-log-line.test.ts` - ✅ Build succeeds: `pnpm build` - ✅ Linters pass: `pnpm check` - ✅ Verified log output shows no subsystem duplication <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR removes tslog’s `prefix` option from `getChildLogger()` so that child-logger bindings are carried only via `_meta.name` (and therefore the CLI’s label extraction), eliminating the duplicated subsystem string that previously appeared in positional log args. Tests in `src/logging/parse-log-line.test.ts` are updated to reflect the new emitted JSON shape: the message is now just the original first positional argument (e.g. `"connected"`) rather than including the redundant `{"subsystem":...}` prefix. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk. - The change is narrowly scoped to removing tslog’s `prefix` injection for child loggers, and the corresponding unit test update aligns with how `parseLogLine` constructs the message from numeric positional fields. No other behavior changes were identified in the affected code paths. - No files require special attention <!-- greptile_other_comments_section --> <!-- /greptile_comment -->