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>

scan_engine.py

@@ -182,11 +182,11 @@ def run_file_scan(source: dict):
     _db_scan_id: int | None = None
     if _db:
         try:
-            _db_scan_id = _db.begin_scan(
-                sources=[source.get("source_type", "local")],
-                user_count=0,
-                options=source,
-            )
+            _db_scan_id = _db.begin_scan({
+                "sources":  [source.get("source_type", "local")],
+                "user_ids": [],
+                "options":  source,
+            })
         except Exception as e:
             logger.error("[db] start_scan failed: %s", e)