chore: vendor all CDN assets locally; reorganise assets into css/ and js/

All third-party assets are now self-hosted — zero external requests at runtime.

CSS (assets/css/):
  - modern-normalize.min.css  (was assets/)
  - common.css, admin.css, main.css, search.css, tfe.css, apropos.css  (was assets/)
  - easymde.min.css 2.20.0  (was cdn.jsdelivr.net)
  - font-awesome.min.css 4.7.0  (was maxcdn.bootstrapcdn.com; injected at runtime by EasyMDE)

JS (assets/js/):
  - easymde.min.js 2.20.0  (was cdn.jsdelivr.net)

Fonts (assets/fonts/fontawesome/):
  - fontawesome-webfont.{eot,woff2,woff,ttf,svg}, FontAwesome.otf 4.7.0

Path fixes:
  - common.css @font-face: ./fonts/ -> ../fonts/ (one level deeper)
  - font-awesome.min.css @font-face: ../fonts/ -> ../fonts/fontawesome/ (dedicated subdir)
  - pages-edit.php: autoDownloadFontAwesome:false added to EasyMDE init to
    suppress the runtime CDN injection that was still present inside easymde.min.js

Reference updates (all now absolute /assets/css/* or /assets/js/*):
  - templates/public/head.php: modern-normalize + common
  - templates/admin/head.php: modern-normalize + admin
  - public/admin/login.php: modern-normalize + admin (standalone head)
  - public/index.php, tfe.php, search.php, apropos.php, licence.php: extraCss paths
  - public/admin/pages-edit.php: extraCss + extraJs (font-awesome, easymde CSS/JS)

Nginx static-file location already covers .css/.js/.woff/.woff2/.ttf/.otf with
30-day cache headers — no nginx config change needed.

public/assets/js/easymde.min.js

@@ -0,0 +1,7 @@
+/**
+ * easymde v2.20.0
+ * Copyright Jeroen Akkerman
+ * @link https://github.com/ionaru/easy-markdown-editor
+ * @license MIT
+ */
+!function(e){if("object"==typeof exports&&"undefined"!=typeof module)module.exports=e();else if("function"==typeof define&&define.amd)define([],e);else{("undefined"!=typeof window?window:"undefined"!=typeof global?global:"undefined"!=typeof self?self:this).EasyMDE=e()}}((function(){return function e(t,n,i){function r(a,l){if(!n[a]){if(!t[a]){var s="function"==typeof require&&require;if(!l&&s)return s(a,!0);if(o)return o(a,!0);var u=new Error("Cannot find module '"+a+"'");throw u.code="MODULE_NOT_FOUND",u}var c=n[a]={exports:{}};t[a][0].call(c.exports,(function(e){return r(t[a][1][e]||e)}),c,c.exports,e,t,n,i)}return n[a].exports}for(var o="function"==typeof require&&require,a=0;a<i.length;a++)r(i[a]);return r}({1:[function(e,t,n){},{}],2:[function(e,t,n){"use strict";var i=e("typo-js");function r(e){"function"==typeof(e=e||{}).codeMirrorInstance&&"function"==typeof e.codeMirrorInstance.defineMode?(String.prototype.includes||(String.prototype.includes=function(){return-1!==String.prototype.indexOf.apply(this,arguments)}),e.codeMirrorInstance.defineMode("spell-checker",(function(t){if(!r.aff_loading){r.aff_loading=!0;var n=new XMLHttpRequest;n.open("GET","https://cdn.jsdelivr.net/codemirror.spell-checker/latest/en_US.aff",!0),n.onload=function(){4===n.readyState&&200===n.status&&(r.aff_data=n.responseText,r.num_loaded++,2==r.num_loaded&&(r.typo=new i("en_US",r.aff_data,r.dic_data,{platform:"any"})))},n.send(null)}if(!r.dic_loading){r.dic_loading=!0;var o=new XMLHttpRequest;o.open("GET","https://cdn.jsdelivr.net/codemirror.spell-checker/latest/en_US.dic",!0),o.onload=function(){4===o.readyState&&200===o.status&&(r.dic_data=o.responseText,r.num_loaded++,2==r.num_loaded&&(r.typo=new i("en_US",r.aff_data,r.dic_data,{platform:"any"})))},o.send(null)}var a='!"#$%&()*+,-./:;<=>?@[\\]^_`{|}~ ',l={token:function(e){var t=e.peek(),n="";if(a.includes(t))return e.next(),null;for(;null!=(t=e.peek())&&!a.includes(t);)n+=t,e.next();return r.typo&&!r.typo.check(n)?"spell-error":null}},s=e.codeMirrorInstance.getMode(t,t.backdrop||"text/plain");return e.codeMirrorInstance.overlayMode(s,l,!0)}))):console.log("CodeMirror Spell Checker: You must provide an instance of CodeMirror via the option `codeMirrorInstance`")}r.num_loaded=0,r.aff_loading=!1,r.dic_loading=!1,r.aff_data="",r.dic_data="",r.typo,t.exports=r},{"typo-js":16}],3:[function(e,t,n){(function(e){"use strict";function t(t,n){clearTimeout(n.timeout),e.off(window,"mouseup",n.hurry),e.off(window,"keyup",n.hurry)}e.defineOption("autoRefresh",!1,(function(n,i){n.state.autoRefresh&&(t(0,n.state.autoRefresh),n.state.autoRefresh=null),i&&0==n.display.wrapper.offsetHeight&&function(n,i){function r(){n.display.wrapper.offsetHeight?(t(0,i),n.display.lastWrapHeight!=n.display.wrapper.clientHeight&&n.refresh()):i.timeout=setTimeout(r,i.delay)}i.timeout=setTimeout(r,i.delay),i.hurry=function(){clearTimeout(i.timeout),i.timeout=setTimeout(r,50)},e.on(window,"mouseup",i.hurry),e.on(window,"keyup",i.hurry)}(n,n.state.autoRefresh={delay:i.delay||250})}))})("object"==typeof n&&"object"==typeof t?e("../../lib/codemirror"):CodeMirror)},{"../../lib/codemirror":10}],4:[function(e,t,n){(function(e){"use strict";e.defineOption("fullScreen",!1,(function(t,n,i){i==e.Init&&(i=!1),!i!=!n&&(n?function(e){var t=e.getWrapperElement();e.state.fullScreenRestore={scrollTop:window.pageYOffset,scrollLeft:window.pageXOffset,width:t.style.width,height:t.style.height},t.style.width="",t.style.height="auto",t.className+=" CodeMirror-fullscreen",document.documentElement.style.overflow="hidden",e.refresh()}(t):function(e){var t=e.getWrapperElement();t.className=t.className.replace(/\s*CodeMirror-fullscreen\b/,""),document.documentElement.style.overflow="";var n=e.state.fullScreenRestore;t.style.width=n.width,t.style.height=n.height,window.scrollTo(n.scrollLeft,n.scrollTop),e.refresh()}(t))}))})("object"==typeof n&&"object"==typeof t?e("../../lib/codemirror"):CodeMirror)},{"../../lib/codemirror":10}],5:[function(e,t,n){(function(e){function t(e){e.state.placeholder&&(e.state.placeholder.parentNode.removeChild(e.state.placeholder),e.state.placeholder=null)}function n(e){t(e);var n=e.state.placeholder=document.createElement("pre");n.style.cssText="height: 0; overflow: visible",n.style.direction=e.getOption("direction"),n.className="CodeMirror-placeholder CodeMirror-line-like";var i=e.getOption("placeholder");"string"==typeof i&&(i=document.createTextNode(i)),n.appendChild(i),e.display.lineSpace.insertBefore(n,e.display.lineSpace.firstChild)}function i(e){o(e)&&n(e)}function r(e){var i=e.getWrapperElement(),r=o(e);i.className=i.className.replace(" CodeMirror-empty","")+(r?" CodeMirror-empty":""),r?n(e):t(e)}function o(e){return 1===e.lineCount()&&""===e.getLine(0)}e.defineOption("placeholder","",(function(o,a,l){var s=l&&l!=e.Init;if(a&&!s)o.on("blur",i),o.on("change",r),o.on("swapDoc",r),e.on(o.getInputField(),"compositionupdate",o.state.placeholderCompose=function(){!function(e){setTimeout((function(){var i=!1;Line truncated