Replaced bare prompt() with proper edit form in card modal:
- showEditForm: renders title input + body textarea + assignee field
- saveIssueEdit: PATCH /api/issues/... with title, body, assignee
- 'Annuler' button returns to card detail view
- Old editIssueInline (prompt only) removed
- Added .form-label CSS style
- dashboard.py: decode session cookie and pass user to template
- notes.py: pass user to template (both GET and POST)
- CSS: .header-right flex layout, #user-info styles, min-height instead of fixed height
- Removed duplicate #user-info CSS block
- Login now properly shows admin/Deconnexion after authentication