fix(editor): AI composer 400, slash-menu arrows, drag handle, block outline, hint

- AI (space) -> 400 DeepSeek: fdAgent.generate now uses the clean no-tools
  /api/agent/generate endpoint instead of the tool-enabled conversation engine
  (which sends tools/tool_choice schemas DeepSeek rejects). Fixes the composer,
  Ask AI, AI meeting note and summarize flows.
- Slash menu arrows: selection highlight was invisible on open (nothing marked),
  so up/down appeared dead. Call _rs() on open + after filtering, and give the
  selected item an accent background + left bar. Verified with jsdom harness:
  Down/Up move selection, Enter applies.
- Block outline when selected: suppress focus rings (outline/box-shadow) on all
  editable blocks ([data-bid], .block-content, page title).
- Drag handle (6-dot): add .block-wrapper:hover/:focus-within .block-handle so
  it shows on hover for normal blocks (only column-wrappers showed it before).
- Empty-block hint: brighter (--text-secondary, opacity .75) so the
  "Press space for AI or / for commands" text is clearly visible on empty paras.
- VERSION + app.main -> 5.1.3; CHANGELOG updated.
- 271 tests pass; page renders 200; /api/agent/generate route registered;
  JS validated (node --check + jsdom).

app/templates/agent_panel.html

@@ -457,44 +457,24 @@
           self.setComposerText(t);
           setTimeout(function(){ self.send(); }, 60);
         };
+        // Headless text generation (no tools) via /agent/generate — the clean
+        // path used by "Ask AI" / "AI meeting note" / summarization. Sending a
+        // plain write request through the tool-enabled conversation engine sends
+        // a tools/tool_choice schema that some providers (e.g. DeepSeek) reject
+        // with a 400. This endpoint returns {ok, text, offline, model}.
         window.fdAgent.generate = function(message, context){
           message = (message || '').trim();
           if(!message) return Promise.resolve('');
-          var payload = {message: message};
+          var payload = {prompt: message};
           if(context && context.trim()) payload.context = String(context).slice(0, 20000);
-          return fetch('/api/agent/conversations', {
+          return fetch('/api/agent/generate', {
             method:'POST', headers:{'Content-Type':'application/json'},
-            body: JSON.stringify({title:'Agent'})
-          }).then(function(r){ return r.json(); }).then(function(conv){
-            var cid = conv && conv.id;
-            if(!cid) throw new Error('Impossible de créer une conversation agent');
-            return fetch('/api/agent/conversations/' + cid + '/run', {
-              method:'POST', headers:{'Content-Type':'application/json'}, body: JSON.stringify(payload)
-            }).then(function(resp){
-              if(!resp.ok){ return resp.json().then(function(j){ throw new Error(j.detail || ('HTTP ' + resp.status)); }); }
-              var reader = resp.body.getReader();
-              var dec = new TextDecoder();
-              var buf = '', finalText = '', lastError = '';
-              function pump(){
-                return reader.read().then(function(res){
-                  if(res.done){ if(lastError) throw new Error(lastError); return finalText; }
-                  buf += dec.decode(res.value, {stream:true});
-                  var parts = buf.split('\n\n');
-                  buf = parts.pop();
-                  for(var i=0;i<parts.length;i++){
-                    var line = parts[i].replace(/^data:\s*/, '').trim();
-                    if(!line) continue;
-                    try{
-                      var ev = JSON.parse(line);
-                      if(ev.type === 'final') finalText = ev.content || '';
-                      else if(ev.type === 'error') lastError = ev.message || 'Erreur agent';
-                    }catch(e){}
-                  }
-                  return pump();
-                });
-              }
-              return pump();
-            });
+            body: JSON.stringify(payload)
+          }).then(function(resp){
+            return resp.json();
+          }).then(function(d){
+            if(d && d.ok){ return d.text || ''; }
+            throw new Error((d && d.error) ? d.error : 'Erreur IA');
           });
         };
       },