feat: Add comprehensive documentation suite and reorganize project structure

- Created complete documentation in docs/ directory
- Added PROJECT_OVERVIEW.md with feature highlights and getting started guide
- Added ARCHITECTURE.md with system design and technical details
- Added SECURITY.md with comprehensive security implementation guide
- Added DEVELOPMENT.md with development workflows and best practices
- Added DEPLOYMENT.md with production deployment instructions
- Added API.md with complete REST API documentation
- Added CONTRIBUTING.md with contribution guidelines
- Added CHANGELOG.md with version history and migration notes
- Reorganized all documentation files into docs/ directory for better organization
- Updated README.md with proper documentation links and quick navigation
- Enhanced project structure with professional documentation standards

f_templates/tpl_backend/tpl_headernav_pop.tpl

@@ -0,0 +1,40 @@
+<div class="tp-h">{$smarty.session.ADMIN_NAME}</div>
+<div class="tp-menu">
+
+<div class="clearfix"></div>
+<ul class="accordion tacc" id="top-session-accordion">
+
+<li class=""><a class="dcjq-parent" href="{$backend_url}/{href_entry key="be_dashboard"}"><i class="icon-pie"></i> {lang_entry key="backend.menu.dash"}</a></li>
+<li class=""><a class="dcjq-parent" href="{$backend_url}/{href_entry key="be_subscribers"}?rg=1"><i class="icon-pie"></i> {lang_entry key="backend.menu.ps.dashboard"}</a></li>
+<li class=""><a class="dcjq-parent" href="{$backend_url}/{href_entry key="be_tokens"}?rg=1"><i class="icon-pie"></i> {lang_entry key="backend.menu.ps.token"}</a></li>
+
+<li class="">
+	<a class="dcjq-parent a-dt" href="javascript:;" rel="nofollow"><i class="icon-contrast"></i> {lang_entry key="frontend.global.darktheme"}: <span id="dark-mode-state-text">{if $theme_name_be|strpos:'dark'===0}{lang_entry key="frontend.global.on.text"}{else}{lang_entry key="frontend.global.off.text"}{/if}</span><i class="iconBe-chevron-right place-right"></i></a>
+</li>
+<li id="l-dt" style="display:none">
+	<div class="dm-wrap">
+		<div class="dm-head dm-head-dt"><i class="icon-arrow-left2"></i> {lang_entry key="frontend.global.darktheme"}</div>
+		<p>{lang_entry key="frontend.global.darktheme.tip1"}<br><br>{lang_entry key="frontend.global.darktheme.tip2"}
+		<div>
+			<span class="label">{lang_entry key="frontend.global.darktheme"}</span>
+			{insert name="themeSwitch"}
+		</div>
+	</div>
+</li>
+{if $smarty.session.lang_count gt 1}
+<li class="">
+	{insert name="langInit"}
+</li>
+{/if}
+<li class=""><a class="dcjq-parent" href="{$backend_url}/{href_entry key="signout"}"><i class="icon-exit"></i> {lang_entry key="frontend.global.signout"}</a></li>
+</ul>
+</div>
+
+{literal}
+<script type="text/javascript">
+$('a.a-dt').click(function(){$('#top-session-accordion li').hide();$('#l-dt').show()});
+$('.dm-head-dt').click(function(){$('#top-session-accordion li').show();$('#l-dt, #l-ln').hide()});
+$('a.a-ln').click(function(){$('#top-session-accordion li').hide();$('#l-ln').show()});
+$('.dm-head-ln').click(function(){$('#top-session-accordion li').show();$('#l-ln, #l-dt').hide()});
+</script>
+{/literal}