feat: add About well to settings with build info and debug easter egg

Add a new well at the bottom of the settings view that displays:
- License (GPL-3.0)
- Author (sneak)
- Version (from package.json)
- Build date (injected at build time)
- Git commit short hash (linked to Gitea commit URL)

Build-time injection: build.js now reads the git commit hash and version
from package.json, injecting them via esbuild define constants. The
Dockerfile and Makefile pass commit hashes as build args so the info is
available even when .git is excluded from the Docker context.

Easter egg: clicking the version number 10 times reveals a hidden debug
well below the About well, containing a toggle for debug mode. The debug
mode flag is persisted in state and enables verbose console logging via
the runtime debug flag in the logger.

closes #144

src/popup/index.html

@@ -1002,6 +1002,54 @@
                     </p>
                     <div id="settings-denied-sites"></div>
                 </div>
+
+                <div class="bg-well p-3 mx-1 mb-3">
+                    <h3 class="font-bold mb-1">About</h3>
+                    <div class="text-xs">
+                        <div class="mb-1">
+                            <span class="text-muted">License:</span>
+                            <span id="about-license"></span>
+                        </div>
+                        <div class="mb-1">
+                            <span class="text-muted">Author:</span>
+                            <span id="about-author"></span>
+                        </div>
+                        <div class="mb-1">
+                            <span class="text-muted">Version:</span>
+                            <span
+                                id="about-version"
+                                class="cursor-pointer select-none"
+                            ></span>
+                        </div>
+                        <div class="mb-1">
+                            <span class="text-muted">Build date:</span>
+                            <span id="about-build-date"></span>
+                        </div>
+                        <div>
+                            <span class="text-muted">Commit:</span>
+                            <a
+                                id="about-commit-link"
+                                class="underline decoration-dashed"
+                                target="_blank"
+                                rel="noopener noreferrer"
+                            ></a>
+                        </div>
+                    </div>
+                </div>
+
+                <div
+                    id="settings-debug-well"
+                    class="bg-well p-3 mx-1 mb-3"
+                    style="display: none"
+                >
+                    <h3 class="font-bold mb-1">Debug</h3>
+                    <label
+                        class="text-xs flex items-center gap-1 cursor-pointer"
+                    >
+                        <input type="checkbox" id="settings-debug-mode" />
+                        Enable debug mode
+                    </label>
+                </div>
             </div>
 
             <!-- ============ DELETE WALLET CONFIRM ============ -->