[BUG] NonCommittingMcpResponseDecorator never releases collected DataBuffers (pooled buffer leak)

- severity: High
- files: `shenyu-plugin/shenyu-plugin-mcp-server/src/main/java/org/apache/shenyu/plugin/mcp/server/response/NonCommittingMcpResponseDecorator.java:146-156`
- description: `aggregateDataBuffers` reads bytes from each `DataBuffer` via `buffer.read(bytes)` but never calls `DataBufferUtils.release(buffer)`. The `collectList()` collects all buffers; after processing they should be released. Since this is a "non-committing" decorator (doesn't write to underlying response), the buffers are never consumed by a downstream writer.
- impact: Pooled direct-memory leak proportional to response size on every Streamable HTTP tool call.
- suggested_fix: Release each buffer after reading in `aggregateDataBuffers`, or use `DataBufferUtils.releaseConsumer`.
- confidence: High
- related_existing: none

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_Identified during the 2026-08-02 deep re-scan; full list in [`docs/scan2-2026-08-02/00-consolidated-critical-high.md`](docs/scan2-2026-08-02/00-consolidated-critical-high.md)._

Open shenyu-plugin/shenyu-plugin-mcp-server/src/main/java/org/apache/shenyu/plugin/mcp/server/response/NonCommittingMcpResponseDecorator.java around lines 146-156 and inspect aggregateDataBuffers. Verify how collected DataBuffers are handled after their bytes are read; done means the non-committing response no longer leaks pooled buffers and the relevant project tests pass.

Written by the indexing model from the issue text.