feat: OpenClaw session import with sorted history

Backend:
- New OpenClawEndpoint with GET /api/openclaw/sessions and POST /api/openclaw/import
- Lists all OpenClaw sessions with preview messages, model, summary
- Imports user/assistant text messages (skips tool-use/tool-result)
- Cleans user messages (removes webchat prefixes, cron tags, conversation info blocks)
- Re-import support: deletes previous openclaw-import chains before importing
- New DatabaseService methods: CreateChainForImport, CreateMessageForImport, DeleteOpenClawImport
- Added SortKey to MessageRecord (computed: openclaw-import gets id-10B, else id)

History sorting:
- OpenClaw-imported messages always appear before native messages
- Sort by CASE WHEN tag='openclaw-import' THEN id-10000000000 ELSE id END
- Cursor-based paging updated from beforeId/afterId to beforeSortKey/afterSortKey
- All history queries (GetLatestActive, Before, After, CountBefore) updated

Frontend:
- Dashboard: new 'OpenClaw Import' menu item in session card dropdown
- Modal: shows OpenClaw sessions with metadata, summary, preview messages
- Imported messages display blue 'OC' badge in chat
- API functions: apiGetOpenclawSessions, apiImportOpenclawSession
- History paging updated to use sortKey cursors

wwwroot/js/api.js

@@ -96,16 +96,16 @@ async function apiDeleteAgent(agentId) {
   return fetch(`/api/agents/${agentId}`, { method: 'DELETE' });
 }
 
-async function apiHistory(sessionId, beforeId, includeDeleted = false) {
+async function apiHistory(sessionId, beforeSortKey, includeDeleted = false) {
   let url = `/api/history?sessionId=${sessionId}`;
-  if (beforeId) url += `&beforeId=${beforeId}`;
+  if (beforeSortKey) url += `&beforeSortKey=${beforeSortKey}`;
   if (includeDeleted) url += `&includeDeleted=true`;
   const resp = await fetch(url);
   return resp.json();
 }
 
-async function apiHistoryPoll(sessionId, afterId, includeDeleted = false) {
-  let url = `/api/history/poll?sessionId=${sessionId}&afterId=${afterId}`;
+async function apiHistoryPoll(sessionId, afterSortKey, includeDeleted = false) {
+  let url = `/api/history/poll?sessionId=${sessionId}&afterSortKey=${afterSortKey}`;
   if (includeDeleted) url += `&includeDeleted=true`;
   const resp = await fetch(url);
   return resp.json();
@@ -544,6 +544,30 @@ async function apiKreaGenerate(prompt, model, width, height) {
   return resp.json();
 }
 
+// ── OpenClaw Import API ──
+
+async function apiGetOpenclawSessions() {
+  const resp = await fetch('/api/openclaw/sessions');
+  if (!resp.ok) {
+    const err = await resp.json().catch(() => ({}));
+    throw new Error(err.error || 'OpenClaw-Sessions konnten nicht geladen werden');
+  }
+  return resp.json();
+}
+
+async function apiImportOpenclawSession(openclawSessionId, sessionId) {
+  const resp = await fetch('/api/openclaw/import', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ openclawSessionId, sessionId })
+  });
+  if (!resp.ok) {
+    const err = await resp.json().catch(() => ({}));
+    throw new Error(err.error || 'Import fehlgeschlagen');
+  }
+  return resp.json();
+}
+
 // ── Backup API ──
 
 async function apiBackupDb() {