Add comprehensive architecture documentation and related scripts

- Introduced multiple architecture documentation files covering building block view, runtime view, deployment view, concepts, architecture decisions, quality requirements, technical risks, glossary, UI and styling, testing, CI, and development setup.
- Migrated existing content from `architecture_overview.md` and `implementation_plan.md` into structured documentation.
- Created scripts for checking broken links in documentation and formatting Markdown files for consistency.
- Updated quickstart guide to provide clearer setup instructions and usage overview.
- Removed outdated MVP features and testing strategy documents to streamline documentation.

docs/architecture/09_architecture_decisions.md

@@ -0,0 +1,5 @@
+# 09 — Architecture Decisions
+
+Status: skeleton
+
+Record important architectural decisions, their rationale, and alternatives considered.