initial project scaffold

Rust workspace with nomina-core (rename engine) and nomina-app (Tauri v2 shell).
React/TypeScript frontend with tabbed rule panels, virtual-scrolled file list,
and Zustand state management. All 9 rule types implemented with 25 passing tests.

ui/src/components/rules/ExtensionTab.tsx

@@ -0,0 +1,71 @@
+import { useRuleStore } from "../../stores/ruleStore";
+import type { ExtensionConfig, StepMode } from "../../types/rules";
+
+const extModes = ["Same", "Lower", "Upper", "Title", "Extra", "Remove", "Fixed"] as const;
+
+export function ExtensionTab() {
+  const rule = useRuleStore((s) => s.rules.extension) as ExtensionConfig;
+  const updateRule = useRuleStore((s) => s.updateRule);
+
+  const update = (changes: Partial<ExtensionConfig>) => updateRule("extension", changes);
+
+  return (
+    <div className="flex flex-col gap-3 text-xs">
+      <div className="flex gap-3 items-end">
+        <label className="flex flex-col gap-1 w-40">
+          <span style={{ color: "var(--text-secondary)" }}>Extension mode</span>
+          <select
+            value={rule.mode}
+            onChange={(e) => update({ mode: e.target.value as ExtensionConfig["mode"] })}
+            className="px-2 py-1.5 rounded border"
+            style={{
+              background: "var(--bg-primary)",
+              borderColor: "var(--border)",
+              color: "var(--text-primary)",
+            }}
+          >
+            {extModes.map((m) => (
+              <option key={m} value={m}>{m}</option>
+            ))}
+          </select>
+        </label>
+
+        {(rule.mode === "Fixed" || rule.mode === "Extra") && (
+          <label className="flex flex-col flex-1 gap-1">
+            <span style={{ color: "var(--text-secondary)" }}>
+              {rule.mode === "Extra" ? "Extra extension" : "New extension"}
+            </span>
+            <input
+              type="text"
+              value={rule.fixed_value}
+              onChange={(e) => update({ fixed_value: e.target.value })}
+              className="px-2 py-1.5 rounded border"
+              style={{
+                background: "var(--bg-primary)",
+                borderColor: "var(--border)",
+                color: "var(--text-primary)",
+              }}
+              placeholder="e.g. bak, txt..."
+            />
+          </label>
+        )}
+      </div>
+
+      <div className="flex items-center gap-2">
+        <div className="flex-1" />
+        <span style={{ color: "var(--text-secondary)" }}>Mode:</span>
+        {(["Simultaneous", "Sequential"] as StepMode[]).map((mode) => (
+          <label key={mode} className="flex items-center gap-1 cursor-pointer">
+            <input
+              type="radio"
+              name="ext-mode"
+              checked={rule.step_mode === mode}
+              onChange={() => update({ step_mode: mode })}
+            />
+            <span>{mode}</span>
+          </label>
+        ))}
+      </div>
+    </div>
+  );
+}