feat(tests): migrate to global "setups" system for test configuration

This PR refactors the integration test system from suite-specific "contexts" to global "setups".
This provides better separation of concerns: **suites = what to test, setups = how to configure.**

Key changes:
- New `tests/integration/setups.py` with global, reusable configurations (ollama, vllm, gpt, claude)
- Simplified `tests/integration/suites.py` to only define test collection roots + default setup references
- Updated CLI from `--context` to `--setup` parameter that works with any suite
- Modified `scripts/integration-tests.sh` to use `--test-setup` instead of `--test-context`
- Updated documentation to reflect the new global setup system

Benefits:
- Setups can be reused across multiple suites (e.g., use "gpt" with any suite)
- Clear separation between test selection (suites) and configuration (setups)
- Easier to add new configurations without modifying existing suites
- Centralized configuration management

Usage examples:
- `pytest tests/integration --suite=responses --setup=gpt`
- `pytest tests/integration --suite=vision --setup=ollama`
- `pytest tests/integration --suite=base --setup=vllm`

.github/actions/setup-ollama/action.yml

@@ -1,7 +1,7 @@
 name: Setup Ollama
 description: Start Ollama
 inputs:
-  test-suite:
+  suite:
     description: 'Test suite to use: base, responses, vision, etc.'
     required: false
     default: ''
@@ -11,7 +11,7 @@ runs:
     - name: Start Ollama
       shell: bash
       run: |
-        if [ "${{ inputs.test-suite }}" == "vision" ]; then
+        if [ "${{ inputs.suite }}" == "vision" ]; then
           image="ollama-with-vision-model"
         else
           image="ollama-with-models"