Add in-app changelog viewer and repo CHANGELOG.md

- Added CHANGELOG constant to launcher with version history
- Added 'Changelog' button to header bar (opens formatted dialog)
- Title bar now shows version number (v2.0.0)
- Added CHANGELOG.md to repo root
- Rebuilt .deb with latest sources

src/codex-launcher-gui

@@ -23,6 +23,22 @@ model_provider = ""
 model_catalog_json = ""
 """
 
+CHANGELOG = [
+    ("2.0.0", "2026-05-19", [
+        "Initial release: multi-provider Codex Launcher",
+        "Translation proxy: Responses API to Chat Completions + Anthropic Messages",
+        "GTK endpoint manager with 10+ provider presets",
+        "Codex Default mode (built-in OAuth, zero config)",
+        "Browser UA injection for Cloudflare-protected providers (OpenCode)",
+        "Streaming SSE, tool calls, reasoning content support",
+        "Profile backup/import, model auto-fetch, bulk import",
+        "Refresh Models in background thread",
+        "URL normalization to prevent double-path bugs",
+        "Config backup/restore around sessions",
+        ".deb installer package",
+    ]),
+]
+
 PROVIDER_PRESETS = {
     "Custom": {
         "backend_type": "openai-compat",
@@ -432,9 +448,12 @@ class LauncherWin(Gtk.Window):
         # header row
         hdr = Gtk.Box(spacing=8)
         vbox.pack_start(hdr, False, False, 0)
-        lbl = Gtk.Label(label="<b>Codex Launcher</b>")
+        lbl = Gtk.Label(label="<b>Codex Launcher v2.0.0</b>")
         lbl.set_use_markup(True)
         hdr.pack_start(lbl, False, False, 0)
+        changelog_btn = Gtk.Button(label="Changelog")
+        changelog_btn.connect("clicked", lambda b: self._show_changelog())
+        hdr.pack_end(changelog_btn, False, False, 0)
         mgr_btn = Gtk.Button(label="Manage Endpoints")
         mgr_btn.connect("clicked", lambda b: self._open_mgr())
         hdr.pack_end(mgr_btn, False, False, 0)
@@ -697,6 +716,36 @@ class LauncherWin(Gtk.Window):
         d.run()
         d.destroy()
 
+    def _show_changelog(self):
+        d = Gtk.Dialog(title="Changelog", transient_for=self, modal=True)
+        d.set_default_size(520, 480)
+        d.add_button("Close", Gtk.ResponseType.CLOSE)
+        area = d.get_content_area()
+        area.set_margin_start(12)
+        area.set_margin_end(12)
+        area.set_margin_top(12)
+        area.set_margin_bottom(12)
+        sw = Gtk.ScrolledWindow()
+        sw.set_policy(Gtk.PolicyType.AUTOMATIC, Gtk.PolicyType.AUTOMATIC)
+        area.pack_start(sw, True, True, 0)
+        buf = Gtk.TextBuffer()
+        tv = Gtk.TextView(buffer=buf)
+        tv.set_editable(False)
+        tv.set_cursor_visible(False)
+        tv.set_wrap_mode(Gtk.WrapMode.WORD_CHAR)
+        sw.add(tv)
+        lines = []
+        for ver, date, items in CHANGELOG:
+            lines.append(f"<b>v{ver}</b>  ({date})")
+            for item in items:
+                lines.append(f"  \u2022 {item}")
+            lines.append("")
+        txt = "\n".join(lines).strip()
+        buf.insert(buf.get_end_iter(), txt)
+        d.show_all()
+        d.run()
+        d.destroy()
+
     # ── launch ───────────────────────────────────────────────────
 
     def _launch(self, target):