Ollama gemma4:12b installed locally but not recognized by llmfit (ollama_name mapping missing for whole Gemma 4 family)

**Environment**
- llmfit 1.1.15
- macOS aarch64
- Apple M4 / 24 GB unified memory
- Ollama installed

**Ollama**
```
$ ollama list
gemma4:12b 4eb23ef187e2 7.6 GB 6 weeks ago
```

**Problem**
```
$ llmfit info "gemma4:12b"
No model found matching 'gemma4:12b'
```

**Investigation**
llmfit's catalog contains Gemma 4 models (`google/gemma-4-E4B-it`, `google/gemma-4-E2B-it`, `google/gemma-4-31B-it`, `google/gemma-4-26B-A4B-it`, plus ~74 community fine-tunes matching `gemma-4-12*`), but grepping the full `llmfit fit --json` output shows `"ollama_name": null` on every single Gemma 4 entry. By contrast, Gemma 2 and Gemma 3 entries do carry a populated `ollama_name` (`gemma2:9b`, `gemma3:12b`, `gemma3:27b`, `gemma3n:e4b`, etc.).

So this isn't a fuzzy-search issue like #315 — hyphenated queries do resolve fine:
```
$ llmfit info "gemma-4-12b"
Multiple models match 'gemma-4-12b'. Please be more specific:
- sakamakismile/Huihui-gemma-4-12B-it-abliterated-NVFP4A16
- r0b0tlab/gemma-4-12B-it-nvfp4
...
```
The colon-tag form used by the official Ollama registry (`gemma4:12b`, and presumably `gemma4:e2b`, `gemma4:e4b`, `gemma4:26b`, `gemma4:31b`) simply has no mapping at all, so `info`/`fit`/`bench`/installed-detection can't resolve or recognize it, regardless of what's already pulled locally.

**Expected**
llmfit should detect the officially distributed Ollama tags under `gemma4:*` as installed models (when present in `ollama list`) and allow `info`/`fit`/`bench` operations on them, the same way it already does for `gemma2:*` and `gemma3:*`.

**Suggested scope**
Since the whole family (`gemma4:e2b`, `e4b`, `12b`, `26b`, `31b`, plus the MLX-tagged variants) shares the same `ollama_name: null` gap, the fix likely belongs at the mapping-table level rather than as a single 12B-only patch.

**Reference**
https://ollama.com/library/gemma4

**Related but distinct**
- #315 (closed) — catalog didn't have Gemma 4 at all; fixed by adding the models.
- #332 (closed) — missing GGUF *download* source mappings; fixed by #955.
- This issue is specifically about the missing `ollama_name` *installed-detection* mapping, which neither of the above touched.