v2.8.2

Update docs and README; remove dev plans

Clean up project docs and frontend artifacts: rewrite README (trimmed content, updated version/quickstart and tech stack), update documentation pages (index.html, architecture.html) and add API and User Manual pages (docs/api.html, docs/manual.html). Remove unused development planning files and example component (deleted plans/* and HelloWorld.vue). Bump frontend asset reference in dist/index.html (CSS hash changed) and rename/move codebase_structure.md. These changes consolidate public docs and remove old roadmap/design notes from the repo.