Show all open (unactioned) items by default, not just the last scan

The default results view loaded only the latest scan session (±300s
window), so items dropped out of sight once a newer scan started — and
a long scheduled scan could show little or nothing on browser open.

Add get_open_items(): every flagged item with no disposition (or status
'unreviewed') across all scans, deduped by id to the latest finished
scan. GET /api/db/flagged now serves it when no ?ref is given; ?ref=N
still loads a specific past session. Frontend loadHistorySession(null)
routes to a new loadOpenItems() loader. Rename the banner button to
"Open items" (da/de/en).

get_session_items() default is unchanged — export.py and
scan_scheduler.py still rely on latest-session for the current scan's
report/email.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

templates/index.html

@@ -375,7 +375,7 @@ document.addEventListener('DOMContentLoaded', applyI18n);
           <button id="historyPickerBtn" type="button" onclick="openHistoryPicker()" style="height:24px;padding:0 10px;background:none;border:1px solid var(--border);color:var(--muted);border-radius:4px;font-size:11px;cursor:pointer" data-i18n="history_btn_sessions">Sessions</button>
           <div id="historyDropdown" style="display:none;position:absolute;right:0;top:calc(100% + 4px);background:var(--surface);border:1px solid var(--border);border-radius:6px;z-index:9999;width:300px;max-height:260px;overflow-y:auto;box-shadow:0 4px 12px rgba(0,0,0,.25)"></div>
         </div>
-        <button id="historyLatestBtn" type="button" onclick="loadHistorySession(null)" style="display:none;height:24px;padding:0 10px;background:none;border:1px solid var(--accent);color:var(--accent);border-radius:4px;font-size:11px;cursor:pointer;flex-shrink:0" data-i18n="history_btn_latest">Latest scan</button>
+        <button id="historyLatestBtn" type="button" onclick="loadHistorySession(null)" style="display:none;height:24px;padding:0 10px;background:none;border:1px solid var(--accent);color:var(--accent);border-radius:4px;font-size:11px;cursor:pointer;flex-shrink:0" data-i18n="history_btn_latest">Open items</button>
       </div>
 
       <!-- Filter bar — full width, above grid + preview -->