refactor: web-ai V1 assets → signal_v1/ (graduation prep)

Atomic mv of root V1 assets (main_server.py + modules/ + data/ +
tests/ + entry scripts + docs + logs) into signal_v1/ subdirectory.
load_dotenv() updated to load web-ai/.env explicitly via Path.

Adds web-ai/CLAUDE.md (workspace guide) and web-ai/start.bat
(signal_v1 entry wrapper). Prepares for signal_v2/ Phase 2.

Tests: signal_v1/tests/unit baseline preserved (no regression).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

start.bat

@@ -0,0 +1,3 @@
+@echo off
+cd /d "%~dp0\signal_v1"
+python main_server.py