merge: cherry-pick e1b96310 (security + type-safety + auth middleware) from web-cad
Brings the following 28.06 improvements into web-cad-neu:
- backend/src/auth/authMiddleware.ts: shared requireAuth/requireAdmin middleware
- backend/src/routes/users.ts: admin role checks (critical security fix)
- 6 routes (projects, drawings, elements, layers, blocks, settings): requireAuth
- server.ts: per-route auth (defense-in-depth alongside global hook)
- 6 test files: auth setup + 401 tests
- Frontend: type safety fixes (App.tsx, RenderEngine, SnapEngine, etc.)
- 10 components: SVG stroke-width/linecap/linejoin -> camelCase
- PropertiesPanel: formatPos/formatDim/parseNum helpers
- LayerPanel: aria-labels
- WORKLOG.md: historical worklog from 28.06
Conflicts resolved (4 blocks, all kept HEAD + e1b96310 improvements):
- LayerPanel.tsx: kept HEAD display:flex + e1b96310 aria-label
- PropertiesPanel.tsx: kept HEAD onDelete handler + e1b96310 formatPos helpers
- PropertiesPanel.tsx: kept HEAD delete button (feature) + full inline styles
- Topbar.tsx: kept HEAD onClick + e1b96310 camelCase SVG attrs
Refs: CODE_ANALYSIS.md (Issue #1 partially improved), e1b96310
Leopoldadmin
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