### What problem does this PR solve?
Part of #15853 (provider model-list refactor).
Refactors **Ollama** `ListModels` onto the shared `ParseListModel`
pattern and fixes two correctness issues:
- **Endpoint:** switch the models suffix from `api/ps` (only
currently-running models) to `api/tags` (all installed models) — the
latter is what a model picker should show.
- **Parsing:** Ollama returns `{"models":[{"name","model"}]}`, a
non-OpenAI shape. Decode it into a typed struct, map the names into
`ModelList`, then enrich through `ParseListModel`. This removes the
previous unchecked type assertions (`result["models"].([]interface{})` /
`.(map[string]interface{})` / `.(string)`) that **panicked** when the
body was missing the `models` array or any field, and adds a fallback to
the `model` field when `name` is blank.
- Drops the no-op GET request body and a dead base-URL reassignment.
#### Drive-by fix
Shared gitee_test.go `DSModelList` -> `ModelList` compile fix (renamed
in #15900) so the models test package builds; auto-resolves against the
sibling #15853 PRs.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] Refactoring
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