fix: handle Copilot session-state without SQLite DB

[erSpell]

Summary

Preserve POSIX/WSL-style Copilot CLI workspace labels on Windows instead of rewriting leading slashes.
Add regression coverage for health discovery when Copilot CLI session-state events exist without the legacy SQLite session-store.db.
Relevant regression/provider tests and lint successful. The local suite excluding symlink-creation tests passed. The excluded symlink tests require Windows symlink privileges in this environment and are unrelated to the session-state fallback fix.

Tests

. .venv/Scripts/activate && python -m pytest src/session_recall/tests/test_provider_backends.py src/session_recall/tests/test_health_schema_multistorage.py -q
. .venv/Scripts/activate && python -m compileall -q src/session_recall && python -m ruff check src
. .venv/Scripts/activate && python -m pytest src/session_recall/tests -q -k 'not symlink'
. .Full Windows local testing excludes symlink tests
. .Closes [Bug] database not found. Copilot changed storage format from session-store.db to session-state folder #19