Ollama native adapter (#41)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>
Co-committed-by: dev_agent <dev_agent@cubecraftlabs.com>

internal/ai/llm/ollama/testdata/README.md

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+# Ollama adapter fixtures
+
+These are the native Ollama API response bodies the contract tests in
+`ollama_test.go` replay. They are **not live captures**. Product AI is tested
+with fakes and live vendor calls are opt-in, so no request was sent to an
+Ollama server to make them. Each fixture is a sanitized adaptation of the
+response shapes in Ollama's public API documentation
+(<https://github.com/ollama/ollama/blob/main/docs/api.md>):
+
+- Chat, non-streaming: `POST /api/chat` with `"stream": false`.
+- Structured outputs: `POST /api/chat` with a JSON schema in `"format"`.
+- List local models: `GET /api/tags`.
+- Errors: a JSON `{"error": "..."}` body with a non-2xx status; a model
+  that is not pulled is HTTP 404.
+
+Sanitizing:
+
+- Timestamps, durations, sizes, digests and token counts are illustrative
+  values in the documented format, not values from a real server.
+- Message content is replaced with MealQuest dinner text.
+- Ollama takes no credentials, so none appear.
+
+Below, *not in the public example* marks values that were added for a test
+case and do not come from the documented example.
+
+| Fixture | Case | Shape | Not in the public example |
+| --- | --- | --- | --- |
+| `chat_text.json` | Success | Finished chat message, `done_reason: stop`, `prompt_eval_count` and `eval_count`. | — |
+| `chat_schema.json` | Schema output | Finished chat message whose content is a JSON object string. | The dinner object. |
+| `error_model_not_found.json` | Model missing | `{"error": "model \"…\" not found, try pulling it first"}`, served with HTTP 404. | — |
+| `tags.json` | Model list | `{"models": [...]}` with `name`, `model`, `digest` and `details`. | — |
+
+The unreachable-host case has no fixture: there is no response to record.
+The tests close an `httptest` server and dial its address, so the
+connection is refused, and they hold a reply past a short deadline for the
+timeout.