feat(journal): improve command completion behavior

- Scroll the selected completion item into view
- Filter commands based on prefix when typing a slash command
- Keep completion menu open while typing a command
- Add data attributes to track completion indices for scrolling

src/components/journal/JournalInput.tsx

@@ -12,6 +12,7 @@
 import {
   Component,
   createSignal,
+  createEffect,
   onMount,
   onCleanup,
   Show,
@@ -126,18 +127,34 @@ export const JournalInput: Component = () => {
     revertLatest();
   }
 
+  // ---- Scroll selected completion into view ----
+
+  createEffect(() => {
+    const idx = selectedIdx();
+    if (!showCompletions() || !completionsRef) return;
+    const el = completionsRef.querySelector(`[data-comp-idx="${idx}"]`);
+    if (el) el.scrollIntoView({ block: "nearest" });
+  });
+
   // ---- Completions ----
 
   function buildCompletions(): CompletionItem[] {
     const raw = text().trim();
     const data = comp.data;
-
-    // Show commands when user types /
-    if (raw === "" || raw === "/") {
-      return [
-        { label: "/roll", kind: "command", insertText: "/roll " },
-        { label: "/link", kind: "command", insertText: "/link " },
+    const commands = [
+      { label: "/roll", kind: "command" as const, insertText: "/roll " },
+      { label: "/link", kind: "command" as const, insertText: "/link " },
     ];
+
+    // Show commands when user types / or starts typing a command name
+    if (raw.startsWith("/") && !raw.includes(" ")) {
+      const prefix = raw.toLowerCase();
+      const matches = commands.filter((c) =>
+        c.label.toLowerCase().startsWith(prefix),
+      );
+      return matches.length > 0
+        ? matches
+        : [{ label: "Unknown command", kind: "no-results", insertText: "" }];
     }
 
     // After /roll — show dice suggestions
@@ -226,9 +243,9 @@ export const JournalInput: Component = () => {
         }
         return;
       }
-      // If not open and typing /, open completions
+      // If not open and starts with /, open completions
       const raw = text();
-      if (raw === "/" || raw.startsWith("/roll") || raw.startsWith("/link")) {
+      if (raw.startsWith("/")) {
         e.preventDefault();
         setShowCompletions(true);
         setSelectedIdx(0);
@@ -271,14 +288,8 @@ export const JournalInput: Component = () => {
     const raw = input.value;
     setText(raw);
 
-    // Completions visibility
-    if (
-      raw === "/" ||
-      raw.startsWith("/roll ") ||
-      raw.startsWith("/link ") ||
-      raw === "/roll" ||
-      raw === "/link"
-    ) {
+    // Completions visibility — keep open while user types any /
+    if (raw.startsWith("/")) {
       setShowCompletions(true);
       setSelectedIdx(0);
     } else {
@@ -317,6 +328,7 @@ export const JournalInput: Component = () => {
         <For each={comps}>
           {(item, idx) => (
             <div
+              data-comp-idx={idx()}
               class={`flex items-center gap-2 px-3 py-1.5 cursor-pointer text-sm ${
                 item.kind === "no-results"
                   ? "text-gray-400 italic cursor-default"