[BUG] AbstractLogCollector.close() drops all buffered logs on shutdown

- severity: Medium
- files: `shenyu-plugin/shenyu-plugin-logging/shenyu-plugin-logging-common/.../AbstractLogCollector.java:256-262`
- description: `close()` sets `started = false` (causing `consume()` to exit) then immediately closes the log consume client. Any logs still in `bufferQueue`/`bufferQueueS` are never flushed. On config refresh, `initClient()` calls `close()` before re-init.
- impact: Data loss — all access logs buffered but not yet flushed at config refresh/shutdown are permanently lost.
- suggested_fix: Drain the buffer queue(s) and send a final batch before closing.
- confidence: High
- related_existing: none

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_Identified during the 2026-08-02 deep re-scan; full list in [`docs/scan2-2026-08-02/06-medium-tiers.md`](docs/scan2-2026-08-02/06-medium-tiers.md)._

Start in shenyu-plugin/shenyu-plugin-logging/shenyu-plugin-logging-common/.../AbstractLogCollector.java:256-262 and trace close(), consume(), bufferQueue, and bufferQueueS. Reproduce shutdown or config-refresh behavior, then verify that buffered access logs are retained after close() and before the log consume client is closed.

Written by the indexing model from the issue text.