feat: lock installed skills and show uninstall hint

Author: njb90

src/webview/client/homescreen.ts

@@ -150,9 +150,10 @@ function renderSkillRows(
     const statusText = status === "installed" ? "installed"
                      : status === "partial"   ? "partial"
                      : "—";
-    const checked = status !== "installed" ? "checked" : "";
+    const checked = "checked";
+    const disabled = status === "installed" ? "disabled" : "";
     return `<label class="hs-ai-item">
-      <input type="checkbox" class="hs-ai-cb" data-skill="${escapeHtml(s.dirName)}" ${checked}>
+      <input type="checkbox" class="hs-ai-cb" data-skill="${escapeHtml(s.dirName)}" ${checked} ${disabled}>
       <span class="hs-ai-item-name" title="${escapeHtml(s.description)}">${escapeHtml(s.name)}</span>
       <span class="hs-ai-item-status ${statusClass}">${statusText}</span>
     </label>`;

src/webview/homescreenView.ts

@@ -558,6 +558,14 @@ export class HomescreenViewProvider implements vscode.WebviewViewProvider {
           margin-top: 1px;
         }
 
+        .hs-ai-item input[type="checkbox"]:disabled { opacity: 0.5; cursor: default; }
+        .hs-ai-hint {
+          font-size: 9px;
+          color: var(--vscode-descriptionForeground);
+          margin: 3px 0 0 0;
+          padding: 0;
+        }
+
         /* Progress tick */
         .hs-ai-item-tick {
           flex-shrink: 0;
@@ -705,6 +713,7 @@ export class HomescreenViewProvider implements vscode.WebviewViewProvider {
               <div>
                 <div class="hs-ai-section-head">Skills</div>
                 <div id="hs-ai-skills-list"></div>
+                <div class="hs-ai-hint">Installed skills are locked. Delete files to uninstall.</div>
                 <div class="hs-ai-section-head" style="margin-top:8px">Install for</div>
                 <div id="hs-ai-platform-list"></div>
               </div>