feat(webssh): replace the arrow keys with a Paste button

- drop the four on-screen arrow buttons: a physical keyboard already sends
  them, and the app-cursor mode that made them awkward is handled by keySequence
- add a Paste button that reads the clipboard and hands the text to the shell
  the same way a browser paste does, bracketed paste included
- report a refusal (no secure context or permission) instead of looking dead,
  and fall back to Ctrl+V

docs/web-ssh.md

@@ -52,7 +52,10 @@ Insert/Delete, Tab, Escape and the function keys all send what a terminal sends,
 and the arrows follow the mode a full-screen program asks for.
 
 A small bar above the terminal carries the few keys a browser keeps for itself
-(Ctrl+C, Ctrl+Z, Ctrl+D, Escape, Tab), so they are never out of reach.
+(Ctrl+C, Ctrl+Z, Ctrl+D, Escape, Tab), so they are never out of reach, plus a
+**Paste** button. It reads the clipboard through the browser's clipboard API,
+so it needs a secure context and permission; if either is missing the bar says
+so, and Ctrl+V still works.
 
 Selecting text is left to the browser, so it works like text anywhere: drag
 across the terminal to select, double-click a word, and the selection survives

src/internal/panel/assets/term.js

@@ -664,12 +664,20 @@
     e.preventDefault();
   };
 
+  // paste hands text to the shell the way a browser paste would, including the
+  // bracketed-paste wrapper when the running program asked for it. The toolbar's
+  // Paste button goes through here so it behaves exactly like Ctrl+V.
+  Term.prototype.paste = function (text) {
+    if (!text) return;
+    if (this.modes.bracketed) this._send("\x1b[200~" + text + "\x1b[201~");
+    else this._send(text);
+  };
+
   Term.prototype._onPaste = function (e) {
     var text = (e.clipboardData || window.clipboardData).getData("text");
     if (!text) return;
     e.preventDefault();
-    if (this.modes.bracketed) this._send("\x1b[200~" + text + "\x1b[201~");
-    else this._send(text);
+    this.paste(text);
   };
 
   // keySequence is what a named key sends. The arrows depend on the mode the
@@ -961,6 +969,9 @@
         if (seq !== null) { input(seq); term.focus(); }
       },
       raw: function (text) { input(text); if (term) term.focus(); },
+      // paste is the toolbar's Paste button: clipboard text is delivered the
+      // same way a browser paste is, so bracketed paste still applies.
+      paste: function (text) { if (term) { term.paste(text); term.focus(); } },
       // reconnect is the manual path offered once the retries are exhausted.
       reconnect: function () {
         finished = false;

src/internal/panel/templates/webssh.html

@@ -71,14 +71,11 @@ main>div{height:100%}
   <button type="button" data-key="Escape">Esc</button>
   <button type="button" data-key="Tab">Tab</button>
   <span class="sep"></span>
-  <button type="button" data-key="ArrowLeft">←</button>
-  <button type="button" data-key="ArrowUp">↑</button>
-  <button type="button" data-key="ArrowDown">↓</button>
-  <button type="button" data-key="ArrowRight">→</button>
-  <span class="sep"></span>
   <button type="button" data-ctl="c">^C</button>
   <button type="button" data-ctl="z">^Z</button>
   <button type="button" data-ctl="d">^D</button>
+  <span class="sep"></span>
+  <button type="button" id="pasteBtn">{{if eq .Lang "zh"}}粘贴{{else}}Paste{{end}}</button>
 </div>
 <main><div id="termMount"></div></main>
 <div class="ask" id="ask" hidden>
@@ -165,11 +162,28 @@ main>div{height:100%}
   // A control character cannot be written into an HTML attribute, so the
   // buttons carry a name and the byte is looked up here.
   var CTL={c:"\u0003",z:"\u001a",d:"\u0004"};
+  // The clipboard API needs a secure context and the page's permission, and
+  // neither is guaranteed, so a refusal is reported instead of looking dead.
+  function doPaste(){
+    if(!session)return;
+    if(!(navigator.clipboard&&navigator.clipboard.readText)){
+      setStatus(T('此浏览器不能用按钮粘贴，请按 Ctrl+V / Cmd+V','this browser cannot paste from a button — press Ctrl+V'));
+      session.focus();
+      return;
+    }
+    navigator.clipboard.readText().then(function(text){
+      if(text)session.paste(text); else session.focus();
+    }).catch(function(){
+      setStatus(T('无法读取剪贴板，请按 Ctrl+V / Cmd+V','could not read the clipboard — press Ctrl+V'));
+      session.focus();
+    });
+  }
   keys.addEventListener('mousedown',function(e){ e.preventDefault(); });
   keys.addEventListener('click',function(e){
     var b=e.target.closest('button');
     if(!b||!session)return;
-    if(b.dataset.key)session.key(b.dataset.key);
+    if(b.id==='pasteBtn')doPaste();
+    else if(b.dataset.key)session.key(b.dataset.key);
     else if(b.dataset.ctl&&CTL[b.dataset.ctl])session.raw(CTL[b.dataset.ctl]);
   });