fix(6219): g t opens Knowledge, and the shortcuts overlay lists every g shortcut

g t pushed "/", which now redirects to the dashboard, so it did what g h
does. It pushes /knowledge. The overlay gains g r (Rules) and g g (Graph),
calls g h "Dashboard", and docs/features.md lists g t.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/App.vue

@@ -85,7 +85,7 @@ function onGlobalKeydown(e: KeyboardEvent) {
     switch (e.key) {
       case "h": router.push("/"); break;
       case "n": router.push("/notes"); break;
-      case "t": router.push("/"); break;
+      case "t": router.push("/knowledge"); break;
       case "p": router.push("/projects"); break;
       case "r": router.push("/rules"); break;
       case "g": router.push("/graph"); break;
@@ -182,7 +182,7 @@ onUnmounted(() => {
                 <kbd class="shortcut-key">g</kbd>
                 <span class="shortcut-key-sep">+</span>
                 <kbd class="shortcut-key">h</kbd>
-                <span class="shortcut-desc">Home</span>
+                <span class="shortcut-desc">Dashboard</span>
               </div>
               <div class="shortcut-row">
                 <kbd class="shortcut-key">g</kbd>
@@ -202,6 +202,18 @@ onUnmounted(() => {
                 <kbd class="shortcut-key">p</kbd>
                 <span class="shortcut-desc">Projects</span>
               </div>
+              <div class="shortcut-row">
+                <kbd class="shortcut-key">g</kbd>
+                <span class="shortcut-key-sep">+</span>
+                <kbd class="shortcut-key">r</kbd>
+                <span class="shortcut-desc">Rules</span>
+              </div>
+              <div class="shortcut-row">
+                <kbd class="shortcut-key">g</kbd>
+                <span class="shortcut-key-sep">+</span>
+                <kbd class="shortcut-key">g</kbd>
+                <span class="shortcut-desc">Graph</span>
+              </div>
               <div class="shortcut-row">
                 <kbd class="shortcut-key">g</kbd>
                 <span class="shortcut-key-sep">+</span>
@@ -210,7 +222,7 @@ onUnmounted(() => {
               </div>
               <div class="shortcut-row">
                 <kbd class="shortcut-key">Esc</kbd>
-                <span class="shortcut-desc">Unfocus field → go home</span>
+                <span class="shortcut-desc">Unfocus field → go to the dashboard</span>
               </div>
               <div class="shortcut-row">
                 <kbd class="shortcut-key">?</kbd>