feat(bench): add speed-bench tool service for drafter benchmarks

Runs llama.cpp's SPEED-Bench client (pinned commit) against
llama-server over the compose network, in the tools profile.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitignore

@@ -5,4 +5,6 @@
 data/
 .leankg/
 .cache/
-.qwen/tmp
+.qwen/tmp
+# speed-bench output, see docs/operations.md#speed-bench
+bench-results/