feat: Implement pinned tab manager

This commit introduces a new feature: a pinned tab manager.

- Adds `ZenPinnedTabsObserver` to listen for pinned/unpinned tab events.
- Implements `ZenPinnedTabManager` to handle the logic of managing pinned tabs:
    - Stores pinned tab URLs and titles.
    - Resets the pinned tab to its saved state when closed.
    - Adds a new context menu option to manually reset a pinned tab.
    - Implements a shortcut to close a pinned tab and optionally reset its state.

This feature enhances pinned tab functionality by providing a better user experience for managing and resetting them.

src/ZenPinnedTabManager.mjs

@@ -0,0 +1,148 @@
+class ZenPinnedTabsObserver {
+  static ALL_EVENTS = ['TabPinned', 'TabUnpinned'];
+
+  #listeners = [];
+
+  constructor() {
+    this.#listenPinnedTabEvents();
+  }
+
+  #listenPinnedTabEvents() {
+    const eventListener = this.#eventListener.bind(this);
+    for (const event of ZenPinnedTabsObserver.ALL_EVENTS) {
+      window.addEventListener(event, eventListener);
+    }
+    window.addEventListener('unload', () => {
+      for (const event of ZenPinnedTabsObserver.ALL_EVENTS) {
+        window.removeEventListener(event, eventListener);
+      }
+    });
+  }
+
+  #eventListener(event) {
+    for (const listener of this.#listeners) {
+      listener(event.type, event);
+    }
+  }
+
+  addPinnedTabListener(listener) {
+    this.#listeners.push(listener);
+  }
+}
+
+class ZenPinnedTabManager {
+  init() {
+    this.observer = new ZenPinnedTabsObserver();
+    this.initClosePinnedTabShortcut();
+    this.insertResetTabIntoContextMenu();
+    this.observer.addPinnedTabListener(this.onPinnedTabEvent.bind(this));
+  }
+
+  onPinnedTabEvent(action, event) {
+    const tab = event.target;
+    switch (action) {
+      case "TabPinned":
+        tab.setAttribute("zen-pinned-url", tab.linkedBrowser.currentURI.spec);
+        tab.setAttribute("zen-pinned-title", tab.getAttribute("label"));
+        break;
+      case "TabUnpinned":
+        tab.removeAttribute("zen-pinned-url");
+        tab.removeAttribute("zen-pinned-title");
+        break;
+      default:
+        console.warn('ZenPinnedTabManager: Unhandled tab event', action);
+        break;
+    }
+  }
+
+  resetPinnedTab(tab) {
+
+    if(!tab){
+      tab = TabContextMenu.contextTab;
+    }
+
+    if (!tab || !tab.pinned) {
+      return;
+    }
+
+    const url = tab.getAttribute("zen-pinned-url");
+    const title = tab.getAttribute("zen-pinned-title");
+
+    if (url) {
+      const tabState = SessionStore.getTabState(tab);
+      const state = JSON.parse(tabState);
+
+      let activeIndex = (state.index || state.entries.length) - 1;
+      activeIndex = Math.min(activeIndex, state.entries.length - 1);
+      activeIndex = Math.max(activeIndex, 0);
+      state.entries[activeIndex].url = url;
+      state.entries[activeIndex].title = title;
+      SessionStore.setTabState(tab, state);
+    }
+  }
+
+  initClosePinnedTabShortcut() {
+    let cmdClose = document.getElementById('cmd_close');
+
+    if (cmdClose) {
+      cmdClose.addEventListener('command', this.onCloseTabShortcut.bind(this));
+    }
+  }
+
+  onCloseTabShortcut(event) {
+    if (
+        event &&
+        (event.ctrlKey || event.metaKey || event.altKey) &&
+        gBrowser.selectedTab.pinned
+    ) {
+      const selectedTab = gBrowser.selectedTab;
+      const url = selectedTab.getAttribute("zen-pinned-url");
+      const title = selectedTab.getAttribute("zen-pinned-title");
+
+      let nextTab = gBrowser.tabContainer.findNextTab(selectedTab, {
+        direction: 1,
+        filter: tab => !tab.hidden && !tab.pinned,
+      });
+
+      if (!nextTab) {
+        nextTab = gBrowser.tabContainer.findNextTab(selectedTab, {
+          direction: -1,
+          filter: tab => !tab.hidden && !tab.pinned,
+        });
+      }
+
+      if (selectedTab) {
+        gBrowser.selectedTab = nextTab;
+
+        if (url && Services.prefs.getBoolPref('zen.pinned-tab-manager.reset-pinned-tab-on-close-shortcut',false)) {
+          const tabState = SessionStore.getTabState(selectedTab);
+          const state = JSON.parse(tabState);
+          let activeIndex = (state.index || state.entries.length) - 1;
+          activeIndex = Math.min(activeIndex, state.entries.length - 1);
+          activeIndex = Math.max(activeIndex, 0);
+          state.entries[activeIndex].url = url;
+          state.entries[activeIndex].title = title;
+          SessionStore.setTabState(selectedTab, state);
+        }
+
+        gBrowser.discardBrowser(selectedTab);
+
+        event.stopPropagation();
+        event.preventDefault();
+      }
+    }
+  }
+
+  insertResetTabIntoContextMenu() {
+    console.log('insertResetTabIntoContextMenu');
+    const element = window.MozXULElement.parseXULToFragment(`
+            <menuitem id="context_zen-reset-pinned-tab"
+                      data-lazy-l10n-id="tab-context-zen-reset-pinned-tab"
+                      hidden="true"
+                      oncommand="gZenPinnedTabManager.resetPinnedTab();"/>
+        `);
+    document.getElementById('tabContextMenu').appendChild(element);
+  }
+}
+
+window.gZenPinnedTabManager = new ZenPinnedTabManager();