feat: role-scoped viewer tokens — restrict shared links to student or staff items

Add a Role scope dropdown to the Share modal (All roles / Ansatte / Elever).
Scope is stored as {"role": "student"|"staff"} in viewer_tokens.json and
enforced server-side in GET /api/db/flagged via session["viewer_scope"].
Client-side, #filterRole is pre-set and hidden for scoped viewers so the
constraint cannot be bypassed. Existing tokens and PIN sessions remain
unrestricted. Role badge shown on each scoped token row in the Active links list.

Files: app_config.py, routes/viewer.py, routes/database.py, gdpr_scanner.py,
templates/index.html, static/js/viewer.js, static/js/auth.js,
lang/en.json, lang/da.json, lang/de.json,
CLAUDE.md, CHANGELOG.md, README.md, MANUAL-EN.md, MANUAL-DA.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lang/en.json

@@ -766,6 +766,10 @@
   "share_create_error": "Failed to create link:",
   "share_revoke_confirm": "Revoke this link? Anyone using it will immediately lose access.",
   "share_revoke_error": "Failed to revoke:",
+  "share_scope_lbl": "Role scope",
+  "share_scope_all": "All roles",
+  "share_scope_staff": "Staff",
+  "share_scope_student": "Students",
 
   "viewer_pin_group_title": "Viewer PIN",
   "viewer_pin_desc": "A numeric PIN (4\u20138 digits) that lets anyone open <code style=\"font-size:10px\">/view</code> in a browser for read-only access to results without a token URL.",