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_frontend/tpl_file/tpl_thumbnail.tpl

@@ -0,0 +1,38 @@
+		    <form id="fedit-image-form" class="entry-form-class" method="post" action="" enctype="multipart/form-data">
+			<div id="intabdiv">
+				<article>
+					<h3 class="content-title"><i class="icon-{if $smarty.get.v ne ""}video{elseif $smarty.get.i ne ""}image{elseif $smarty.get.a ne ""}audio{elseif $smarty.get.d ne ""}file{elseif $smarty.get.b ne ""}pencil2{/if}"></i>{lang_entry key="files.text.edit.thumb"}</h3>
+					<div class="line"></div>
+				</article>
+
+			    <div class="left-float left-align wdmax row" id="thumb-change-response"></div>
+			    <div class="left-float left-align wdmax">
+				<div class="row">
+				    <div class="icheck-box up"><input type="radio" name="fedit_image_action" id="fedit-image-upload" value="new" /><label>{lang_entry key="files.text.edit.thumb.text"}</label></div>
+				</div>
+				<div class="row" id="overview-userinfo-file">
+					<div class="left-float left-padding25 hiddenfile">
+					<input type="file" name="fedit_image" id="fedit-image" size="30" onchange="$('#fedit-image-form').submit();" />
+				</div>
+				<br>
+				<center>
+				<button class="save-entry-button button-grey search-button form-button new-image" type="button" onclick="$('.icheck-box.up input').iCheck('check');$('#fedit-image').trigger('click');"><span>{lang_entry key="frontend.global.upload.image"}</span></button>
+				<br><br>
+				<label>{lang_entry key="files.text.thumb.sizes"}</label>
+				</center>
+				<br><br>
+			    </div>
+			    {if $src eq "local"}
+			    <div class="row">
+				<div class="icheck-box"><input type="radio" name="fedit_image_action" id="fedit-image-default" value="default" /><label>{if $smarty.get.v eq ""}{lang_entry key="account.image.upload.default"}{else}{lang_entry key="account.image.upload.grab"}{/if}</label></div>
+			    </div>
+			    <br>
+			    {/if}
+			    <div class="row" id="save-button-row">
+				<button name="save_changes_btn" id="save-image-btn" class="save-entry-button button-grey search-button form-button" type="button" value="1"><span>{lang_entry key="files.text.save.thumb"}</span></button>
+				<a class="link cancel-trigger" href="#"><span>{lang_entry key="frontend.global.cancel"}</span></a>
+			    </div>
+        		</div>
+        	    </form>
+        	    {include file="tpl_frontend/tpl_file/tpl_thumbnail_js.tpl"}
+