chore(tests): normalize recording IDs and timestamps to reduce git diff noise (#3676)

IDs are now deterministic hashes based on request content, and
timestamps are normalized to constants, eliminating spurious changes
when re-recording tests.

## Changes
- Updated `inference_recorder.py` to normalize IDs and timestamps during
recording
- Added `scripts/normalize_recordings.py` utility to re-normalize
existing recordings
- Created documentation in `tests/integration/recordings/README.md`
- Normalized 350 existing recording files

tests/integration/recordings/README.md

@@ -0,0 +1,60 @@
+# Test Recording System
+
+This directory contains recorded inference API responses used for deterministic testing without requiring live API access.
+
+## Structure
+
+- `responses/` - JSON files containing request/response pairs for inference operations
+
+## Recording Format
+
+Each JSON file contains:
+- `request` - The normalized request parameters (method, endpoint, body)
+- `response` - The response body (serialized from Pydantic models)
+
+## Normalization
+
+To reduce noise in git diffs, the recording system automatically normalizes fields that vary between runs but don't affect test behavior:
+
+### OpenAI-style responses
+- `id` - Deterministic hash based on request: `rec-{request_hash[:12]}`
+- `created` - Normalized to epoch: `0`
+
+### Ollama-style responses
+- `created_at` - Normalized to: `"1970-01-01T00:00:00.000000Z"`
+- `total_duration` - Normalized to: `0`
+- `load_duration` - Normalized to: `0`
+- `prompt_eval_duration` - Normalized to: `0`
+- `eval_duration` - Normalized to: `0`
+
+These normalizations ensure that re-recording tests produces minimal git diffs, making it easier to review actual changes to test behavior.
+
+## Usage
+
+### Recording mode
+Set `LLAMA_STACK_TEST_INFERENCE_MODE=record` to capture new responses:
+```bash
+LLAMA_STACK_TEST_INFERENCE_MODE=record pytest tests/integration/
+```
+
+### Replay mode (default)
+Responses are replayed from recordings:
+```bash
+LLAMA_STACK_TEST_INFERENCE_MODE=replay pytest tests/integration/
+```
+
+### Live mode
+Skip recordings entirely and use live APIs:
+```bash
+LLAMA_STACK_TEST_INFERENCE_MODE=live pytest tests/integration/
+```
+
+## Re-normalizing Existing Recordings
+
+If you need to apply normalization to existing recordings (e.g., after updating the normalization logic):
+
+```bash
+python scripts/normalize_recordings.py
+```
+
+Use `--dry-run` to preview changes without modifying files.