fix(image): detect Windows local image refs

[zapabob]

Summary

• Detect native Windows drive-letter image paths in extract_image_refs().
• Keep the existing URL-fragment guard so local path matching does not attach paths from https://... URLs.
• Expand ~/... using HOME when present so tests and Windows shell environments behave predictably.

Why

The v0.15.1 kanban worker image-ref tests exercise local image attachments from task bodies. On Windows, absolute paths such as C:\Users\...\screenshot.png were not matched because the local path regex only handled POSIX /... and ~/... shapes. That caused local image paths to be dropped while URL images still attached.

I searched the upstream issue tracker for Windows extract_image_refs, kanban image Windows, and image path Windows and did not find an existing matching issue.

Verification

• PYTHONUTF8=1 PYTHONIOENCODING=utf-8 .\.venv\Scripts\python.exe scripts\run_tests_parallel.py tests\agent\test_image_routing.py tests\hermes_cli\test_kanban_worker_image_extraction.py -- --tb=short --timeout-method=thread → 86 passed
• .\.venv\Scripts\python.exe -m ruff check agent\image_routing.py tests\agent\test_image_routing.py tests\hermes_cli\test_kanban_worker_image_extraction.py → passed

[teknium1]

Thanks for the focused Windows parity fix. The premise is confirmed on current main: agent/image_routing.py:68-70 still recognizes only POSIX / and ~/ paths, while the kanban worker calls extract_image_refs() on task bodies at cli.py:16065-16090. The gateway already uses the intended drive-letter grammar at gateway/platforms/base.py:3748-3754.

Problems

• This PR changes only agent/image_routing.py; it adds no regression coverage. The existing extractor tests at tests/agent/test_image_routing.py:523-639 cover POSIX paths and URL guarding but not either Windows drive-letter separator form.

Suggested changes

• Add focused tests for C:\\...\\shot.png and C:/.../shot.png, along with C:relative.png non-matching and the existing URL-fragment guard. Matcher-level cases can run cross-platform; add a native-Windows filesystem case if needed for path validation.

Automated hermes-sweeper review.

[teknium1]

Please add regression coverage for both C:\\...\\image.png and C:/.../image.png, plus a relative-drive and URL-fragment negative case. Current extractor tests cover only POSIX-shaped paths.