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/da.json

@@ -766,6 +766,10 @@
   "share_create_error": "Kunne ikke oprette link:",
   "share_revoke_confirm": "Tilbagekald dette link? Alle der bruger det, mister straks adgang.",
   "share_revoke_error": "Kunne ikke tilbagekalde:",
+  "share_scope_lbl": "Rolleomfang",
+  "share_scope_all": "Alle roller",
+  "share_scope_staff": "Ansatte",
+  "share_scope_student": "Elever",
 
   "viewer_pin_group_title": "Seerens PIN",
   "viewer_pin_desc": "En numerisk PIN (4–8 cifre), der lader alle åbne <code style=\"font-size:10px\">/view</code> i en browser for skrivebeskyttet adgang til resultater uden et token-link.",