feat(v1): add replayable video source

docs/07-v1-implementation-plan.md

@@ -132,7 +132,7 @@ git commit -m "feat(v1): add secure configuration baseline"
 - Create: `v1/video_source.py`
 - Create: `v1/tests/test_video_source.py`
 
-- [ ] **Step 1: Write replay and broken-source tests**
+- [x] **Step 1: Write replay and broken-source tests**
 
 ```python
 def test_file_source_emits_monotonic_timestamps(sample_video):
@@ -146,12 +146,12 @@ def test_missing_source_returns_error_state(tmp_path):
     assert source.read().status == SourceStatus.ERROR
 ```
 
-- [ ] **Step 2: Run tests to verify they fail**
+- [x] **Step 2: Run tests to verify they fail**
 
 Run: `python -m pytest v1/tests/test_video_source.py -v`
 Expected: FAIL because `VideoSource` and `SourceStatus` do not exist.
 
-- [ ] **Step 3: Implement the source contract**
+- [x] **Step 3: Implement the source contract**
 
 ```python
 from typing import Optional
@@ -172,12 +172,12 @@ class FramePacket:
 
 `read()` returns an error packet for failures; it never emits a synthetic person or fall event. For RTSP, reconnect with bounded backoff from configuration.
 
-- [ ] **Step 4: Run tests**
+- [x] **Step 4: Run tests**
 
 Run: `python -m pytest v1/tests/test_video_source.py -v`
 Expected: PASS.
 
-- [ ] **Step 5: Commit**
+- [x] **Step 5: Commit**
 
 ```powershell
 git add v1/video_source.py v1/tests/test_video_source.py docs progress.md