tests : update Metal fusion baseline for beam (#30764)

* tests: add beam fusion rows to MTL baseline

Regenerate tests/fusion/MTL.csv with test-fusion --record. The newly
added beam architecture has no baseline rows, so test-fusion fails with
2 failing rows (MUL+ADD x6, RMS_NORM+MUL x25). All other arch counts are
unchanged.

Assisted-by: pi:llama.cpp/ggml-org/Qwen3.8-Flash-Next-GGUF (MacBook, M5 Max, 128GB)

* skills: add update-fusion-table skill

Add a skill for regenerating a per-device test-fusion baseline. It keeps
the workflow from tests/fusion/README.md and the parts that are easy to
get wrong: diff the recorded file before applying it, the distinct
meanings of a FAIL row, and never recording a partial run.

Assisted-by: pi:llama.cpp/ggml-org/Qwen3.8-Flash-Next-GGUF (MacBook, M5 Max, 128GB)

skills/update-fusion-table/SKILL.md

@@ -0,0 +1,39 @@
+---
+name: update-fusion-table
+description: Regenerate a per-device test-fusion baseline (tests/fusion/MTL.csv, ...) after fusion patterns or the dummy-model set change. Use when test-fusion --check fails.
+---
+
+# Update a fusion baseline
+
+`tests/fusion/<BACKEND>.csv` is the `test-fusion` golden baseline: `arch,moe,mode,label,count`,
+where `count` is how many times a fusion label matched per graph run. See `tests/fusion/README.md`.
+
+Re-record only when the counts moved for the reason the contributor intended. A row failing on
+`nmse_fus` (> 1e-4) is a fused-vs-unfused correctness bug, not baseline drift - fix it, never
+record it away.
+
+## Steps
+
+```sh
+cmake -B build -DCMAKE_BUILD_TYPE=Release -DGGML_METAL=ON       # enable the target backend
+cmake --build build --config Release --target test-llama-archs --target test-fusion -j
+
+rm -rf build-ci-models && mkdir -p build-ci-models              # always regenerate
+./build/bin/test-llama-archs -o build-ci-models
+
+D=MTL0; B=tests/fusion/MTL.csv; T=/tmp/$(basename $B)   # keep the target backend/device in sync
+./build/bin/test-fusion --models build-ci-models --device $D --check $B   # read the FAIL rows
+./build/bin/test-fusion --models build-ci-models --device $D --record $T
+diff $B $T
+cp $T $B
+./build/bin/test-fusion --models build-ci-models --device $D --check $B   # 0 failed, exit 0
+```
+
+- Read the diff before applying it. Every added, removed or changed row must be explainable by the
+  change under review; an unexplained row means the run picked up something unintended.
+- `expected 0` in a FAIL row = no baseline row for that label (new arch, or a fusion newly
+  firing); non-zero `expected` = count changed; `fusion ... is no longer matched` = row stopped
+  firing.
+- `--record` rewrites the whole file, so never record a partial run (`--model FILE`, a filtered
+  models dir) - it drops the rows of every architecture that was not run.
+- `--record` marks every row `ok`; only the `--check` run validates.

tests/fusion/MTL.csv

@@ -20,6 +20,8 @@ bailingmoe3         ,1   ,any     ,GATED_DELTA_NET+CPY         ,      1
 bailingmoe3         ,1   ,any     ,MUL+ADD                     ,      2
 bailingmoe3         ,1   ,any     ,RMS_NORM+MUL                ,      8
 bailingmoe3         ,1   ,any     ,RMS_NORM+SCALE              ,      2
+beam                ,0   ,any     ,MUL+ADD                     ,      6
+beam                ,0   ,any     ,RMS_NORM+MUL                ,     25
 bloom               ,0   ,any     ,NORM+MUL+ADD                ,      6
 chatglm             ,0   ,any     ,RMS_NORM+MUL                ,      5
 codeshell           ,0   ,any     ,NORM+MUL+ADD                ,      5