feat: implement file watching functionality in the filesystem module

- Added methods for file watching, including `watch`, `unwatch`, `unwatchAll`, `getWatchCount`, `pollWatch`, `getLastWatchPath`, and `getLastWatchRealPath`.
- Enhanced the `Filesystem` class to support monitoring file changes, allowing for real-time updates.
- Updated the `physfs` implementation to handle file watch targets and events.
- Improved documentation and added unit tests to validate the new file watching features.

Co-authored-by: Cursor <cursoragent@cursor.com>

test/UIPhaseB.cpp

@@ -0,0 +1,110 @@
+#include "zeroerr/assert.h"
+#include "zeroerr/unittest.h"
+
+#include "ui/Component.h"
+#include "ui/Theme.h"
+#include "ui/UI.h"
+#include "ui/UIHost.h"
+#include "ui/UISystem.h"
+#include "ui/Widget.h"
+
+#include <string>
+#include <vector>
+
+using namespace eve::ui;
+
+class InventoryPanel : public Component {
+public:
+    std::vector<std::string> items{"Sword", "Potion"};
+    int gold = 10;
+    bool showExtra = true;
+
+    WidgetDesc build() override {
+        return window("Inventory",
+                      {
+                          text("Gold " + std::to_string(gold), "gold"),
+                          separator("sep"),
+                          listButtons("items", items),
+                          when(showExtra, text("Extra tip", "tip")),
+                          checkbox("Show tip", showExtra, "tipchk", [this](bool v) {
+                              showExtra = v;
+                              setState();
+                          }),
+                      },
+                      "root");
+    }
+};
+
+TEST_CASE("UI.b.listAndWhen") {
+    auto tree = window("W", {
+                                when(false, text("hidden", "h")),
+                                when(true, text("shown", "s")),
+                                listButtons("L", {"a", "b", "c"}),
+                            });
+    UIHost *h = UIHost::createHost("listwhen");
+    h->setTree(std::move(tree));
+    CHECK(h->findById("s") != nullptr);
+    CHECK(h->findById("h") == nullptr);  // when(false) → empty group, no "h"
+    CHECK(h->findById("L/0") != nullptr);
+    CHECK(h->findById("L/2") != nullptr);
+}
+
+TEST_CASE("UI.b.keyReconcilePropsOnly") {
+    UIHost *h = UIHost::createHost("rec");
+    h->setTree(window("W", {text("v1", "label"), button("Go", "btn")}, "root"));
+    bool rebuilt = h->setTreeReconcile(window("W", {text("v2", "label"), button("Go", "btn")}, "root"));
+    CHECK(!rebuilt);  // structure same → props patch
+    CHECK(h->findById("label")->text == "v2");
+
+    rebuilt = h->setTreeReconcile(
+        window("W", {text("v3", "label"), button("Go", "btn"), button("New", "n")}, "root"));
+    CHECK(rebuilt);  // child count changed → full rebuild
+    CHECK(h->findById("n") != nullptr);
+}
+
+TEST_CASE("UI.b.componentRebuild") {
+    InventoryPanel panel;
+    panel.mountAs("inv");
+    UIHost *h = UISystem::findHost("inv");
+    REQUIRE(h != nullptr);
+    CHECK(h->findById("gold")->text == "Gold 10");
+    CHECK(h->findById("items/0") != nullptr);
+
+    panel.gold = 9;
+    panel.items.push_back("Shield");
+    panel.markDirty();
+    CHECK(panel.updateIfDirty());
+    CHECK(h->findById("gold")->text == "Gold 9");
+    CHECK(h->findById("items/2") != nullptr);
+}
+
+TEST_CASE("UI.b.themeAndCheckbox") {
+    UI *ui = UI::create();
+    ui->setThemeLight();
+    CHECK(globalTheme().windowBg[0] > 0.5f);
+    ui->setThemeDark();
+    ui->setNavKeyboard(true);
+    CHECK(globalTheme().navEnableKeyboard);
+
+    ui->mountAs("chk", window("C", {checkbox("Mute", false, "mute")}, "root"));
+    CHECK(ui->current()->findById("mute") != nullptr);
+    CHECK(!ui->current()->findById("mute")->checked);
+    ui->setChecked("mute", true);
+    CHECK(ui->current()->findById("mute")->checked);
+}
+
+TEST_CASE("UI.b.scriptListBuilder") {
+    UI *ui = UI::create();
+    ui->beginBuild();
+    ui->beginWindow("Shop", "root");
+    ui->beginList("goods");
+    ui->addListItem("Apple", "goods/0");
+    ui->addListItem("Bread", "goods/1");
+    ui->end();
+    ui->addSeparator("s");
+    ui->addCheckbox("Member", false, "mem");
+    ui->end();
+    CHECK(ui->mountBuildAs("shop"));
+    CHECK(ui->current()->findById("goods/1") != nullptr);
+    CHECK(ui->current()->findById("mem") != nullptr);
+}