Add cross-file call graph extraction and query APIs (callers, callees,
call paths), decompose monolithic diff.html into modular JS/CSS files,
add Vue-based web-client with Vite build, introduce schema version
management for vector/RxDB stores, add file viewer page, and update
web server to serve Vite build when available.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>