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- Removed outdated MVP features and testing strategy documents to streamline documentation.

scripts/check_docs_links.py

@@ -0,0 +1,43 @@
+"""Simple Markdown link checker for local docs/ files.
+
+Checks only local file links (relative paths) and reports missing targets.
+
+Run from the repository root using the project's Python environment.
+"""
+import re
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parent.parent
+DOCS = ROOT / 'docs'
+
+MD_LINK_RE = re.compile(r"\[([^\]]+)\]\(([^)]+)\)")
+
+errors = []
+
+for md in DOCS.rglob('*.md'):
+    text = md.read_text(encoding='utf-8')
+    for m in MD_LINK_RE.finditer(text):
+        label, target = m.groups()
+        # skip URLs
+        if target.startswith('http://') or target.startswith('https://') or target.startswith('#'):
+            continue
+        # strip anchors
+        target_path = target.split('#')[0]
+        # if link is to a directory index, allow
+        candidate = (md.parent / target_path).resolve()
+        if candidate.exists():
+            continue
+        # check common implicit index: target/ -> target/README.md or target/index.md
+        candidate_dir = md.parent / target_path
+        if candidate_dir.is_dir():
+            if (candidate_dir / 'README.md').exists() or (candidate_dir / 'index.md').exists():
+                continue
+        errors.append((str(md.relative_to(ROOT)), target, label))
+
+if errors:
+    print('Broken local links found:')
+    for src, tgt, label in errors:
+        print(f'- {src} -> {tgt}  ({label})')
+    exit(2)
+
+print('No broken local links detected.')