feat: scan history browser, user-scoped viewer tokens, export fixes, email fixes (v1.6.20)

- Scan history browser (history.js, GET /api/db/sessions, get_sessions(),
  get_session_items(ref_scan_id)) — review any past session without rescanning
- User-scoped viewer tokens (#34) — scope by individual employee across M365
  and GWS; autocomplete from Accounts list; dual-email support
- Fix: GWS scan never marked finished (end_scan → finish_scan) and emitted
  wrong SSE event (scan_done → google_scan_done), excluding GWS items from all
  exports
- Fix: file scan begin_scan called with wrong keyword args (TypeError swallowed),
  so local/SMB items were never written to DB
- Fix: Graph sendMail reported failure on success — _post() now returns {} on
  empty 202 response instead of raising JSONDecodeError
- Fix: Graph error hidden behind generic "No SMTP host" message when both Graph
  and SMTP were unavailable
- Fix: Gmail vs Google Workspace SMTP error messages distinguished by username
  domain; Workspace errors point to admin console, not personal security settings
- Docs: update README, MANUAL-EN, MANUAL-DA, CLAUDE.md, TODO.md, CHANGELOG.md

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

lang/en.json

@@ -103,6 +103,13 @@
   "lbl_time": "Time",
   "lbl_space": "Space",
   "lbl_loading": "Loading…",
+  "history_lbl": "History",
+  "history_items": "items",
+  "history_btn_sessions": "Sessions",
+  "history_btn_latest": "Latest scan",
+  "history_picker_empty": "No past scans",
+  "history_delta_badge": "Delta",
+  "history_latest_badge": "Latest",
   "lbl_blurred": "Blurred",
   "lbl_none": "None",
   "lbl_scanner": "Scanner",
@@ -766,8 +773,14 @@
   "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_lbl": "Scope",
+  "share_scope_all": "All",
+  "share_scope_type_role": "Role",
+  "share_scope_type_user": "User",
+  "share_scope_role_lbl": "Role",
+  "share_scope_user_lbl": "User email",
+  "share_scope_user_placeholder": "alice@school.dk",
+  "share_scope_user_invalid": "Please enter a valid email address for the user scope.",
   "share_scope_staff": "Staff",
   "share_scope_student": "Students",