llm_merge_hpc: the 7B firm-up makes the Fisher-Muller sign decisive

Re-ran the specialist-merge experiment at a capable base (Qwen2.5-7B-Instruct,
200 tests/family) on one L40S GPU of Imperial's CX3 HPC (8 min walltime). The
two caveats the 0.5B prototype left marginal are now resolved:

- "exceeds every parent overall" is clean: both merges 0.87 vs best specialist
  0.77 (+10 pts), and above every specialist on every family.
- dilution vanishes: at 0.5B averaging diluted the lists-specialist
  (0.43->0.26); at 7B the merge beats it (0.62>0.57). Dilution was a
  small-model artefact -- a capable base composes rather than dilutes, which
  softens E4's "merge, don't average" once the parents are strong.

The figure title is now data-driven (reports ">" for 7B, "~" for 0.5B).
Adds the hpc/ smoke job script and the llm_merge walltime trim. Results synced
to results/llm_merge_hpc/ (parquet gitignored per the reproducibility contract).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

results/llm_merge_hpc/manifest.json

@@ -0,0 +1,20 @@
+{
+  "experiment": "llm_merge_hpc",
+  "master_seed": 1,
+  "git_commit": null,
+  "python": "3.11.13",
+  "libraries": {
+    "numpy": "2.4.6",
+    "scipy": "1.17.1",
+    "pandas": "3.0.3",
+    "pyarrow": "24.0.0",
+    "torch": "2.12.1",
+    "transformers": "5.13.0",
+    "peft": "0.19.1"
+  },
+  "rows": 30,
+  "results_sha256": "6cc0a07c66ba92a379d895d6d6707591aced48f06eee895bb4f6c15d12e6e588",
+  "layer": "2",
+  "tier": "llm",
+  "base_model": "Qwen/Qwen2.5-7B-Instruct"
+}