refactor: merge /spark command into /roll

Consolidate the `/spark` command into `/roll` to simplify the CLI.
The `/roll` command now handles both dice notation and spark table
slugs.

- Update `parseInput` to treat `/roll` arguments as a generic string.
- Update `dispatchCommand` to check for spark table matches before
  evaluating dice notation or variable expressions.
- Update command completions to show both dice and spark table
  suggestions under `/roll`.
- Update documentation and UI placeholders to reflect the change.

src/components/journal/command-dispatcher.ts

@@ -87,30 +87,57 @@ export async function dispatchCommand(
 
   // GM: all commands
   if (parsed.type === "roll") {
-    const p = resolveRollPayload(
-      parsed.payload as { notation: string; label?: string },
-    );
+    const arg = (parsed.payload as { arg: string }).arg;
+
+    // Try spark table first: if arg matches a known spark table slug, roll it
+    const match = ctx.sparkTables.find((s) => s.slug === arg);
+    if (match) {
+      try {
+        const csvPath = match.csvPath ?? "";
+        const remix = match.remix ?? false;
+        const p = await resolveSparkPayload({ key: arg, csvPath, remix });
+        const result = sendMessage("spark", p);
+        return finish(unwrap(result));
+      } catch (e) {
+        return finish({
+          ok: false,
+          error: e instanceof Error ? e.message : "种子表掷骰失败",
+        });
+      }
+    }
+
+    // Variable expression (e.g. "2d6 + $mod" or "$hp / 2")
+    if (arg.includes("$")) {
+      try {
+        const ev = evaluateExpression(arg, {
+          lookup: (name: string) => getCombined("$" + name, ctx.variables),
+        });
+        const payload = {
+          notation: arg,
+          label: arg,
+          result: {
+            total: ev.value,
+            detail: "",
+            plainDetail: "",
+            pools: [] as { rolls: number[]; subtotal: number }[],
+          },
+        };
+        const result = sendMessage("roll", payload);
+        return finish(unwrap(result));
+      } catch (e) {
+        return finish({
+          ok: false,
+          error: e instanceof Error ? e.message : "表达式求值失败",
+        });
+      }
+    }
+
+    // Otherwise, treat as a dice expression
+    const p = resolveRollPayload({ notation: arg, label: arg });
     const result = sendMessage("roll", p);
     return finish(unwrap(result));
   }
 
-  if (parsed.type === "spark") {
-    try {
-      const key = (parsed.payload as { key: string }).key;
-      const match = ctx.sparkTables.find((s) => s.slug === key);
-      const csvPath = match?.csvPath ?? "";
-      const remix = match?.remix ?? false;
-      const p = await resolveSparkPayload({ key, csvPath, remix });
-      const result = sendMessage("spark", p);
-      return finish(unwrap(result));
-    } catch (e) {
-      return finish({
-        ok: false,
-        error: e instanceof Error ? e.message : "种子表掷骰失败",
-      });
-    }
-  }
-
   if (parsed.type === "set" || parsed.type === "rolltag") {
     return finish(dispatchSet(parsed.payload as Record<string, unknown>, ctx));
   }