Add IMAP webmail tag, admin/opensource subpage tiers, store/cart, htmleditor, uploads

New __imap*/__smtpsend/__eval Jet tags give templates real IMAP
(list/message/flag/delete/move/search/folders/accounts) and SMTP-send
capability, backing the new /email webmail client (email.jet/
email.menu, assets/images/email.js + newemail.js) and its
mainpagetemplate.jet-based page shell. Most of this tag family's
source was already being built into the live site (Tag.cpp already
registered __imap/__imaplist/__imapmessage/__imapflag/__imapdelete/
__eval) but had never actually been committed; this also registers
and commits the remaining five (__imapmove/__imapfolders/
__imapsearch/__smtpsend/__imapaccounts).

admin.page/admin.menu gain a real subpage tier (admin-email,
admin-newemail, admin-invoices, admin-products, admin-users) replacing
several previously top-level pages, mirrored by a similar
opensource.page subpage tier (opensource-overview/asm1802/barantmail/
jet/serverframework/synthmax) - old top-level pages retired via git
rename (asm1802.page, jet.page, serverframework.page,
admin_invoices.page); barantmail.page is dropped outright, folded into
opensource-barantmail.subpage.

New storefront (store.page, store-createstore.subpage,
barantstore.page) and cart flow (cart.jet, updatecartqty.proc,
removecartitem.proc, editproduct.page/selectproduct.proc/
update_product.proc for inventory maintenance against the barant
database).

New document upload/download manager (documents.jet, documents_api.jet,
documents_upload.proc, documents_delete.proc,
assets/images/documents.js + documents-page.js) with a persistent
floating panel, and a rich-text page editor (htmleditor.jet/.page,
createhtmleditor.proc, savehtmleditor.proc, assets/images/htmleditor.js
+ its icon/logo assets).

SESSIONCTL.tag: login now redirects back to the originally-requested
page instead of always landing on /account ($[start:0] vs $[start]
variable-name mismatch).

main.css/menu.bar/invoices.menu/jet_overview.section/login.menu:
styling and navigation updates for the above; new site assets (fonts,
images, audio) referenced by them.

jetc/build-assets.sh, list_jet_files.sh, lowercase_jet.py,
strip_fragments.py: small dev tooling used while building the above.

__eval.cpp

@@ -0,0 +1,43 @@
+#include "__eval.h"
+#include "Exception.h"
+
+namespace jet {
+
+   // <eval> is not a jet-2.0 addition - it's a genuine jet-1.4 tag that was
+   // simply never implemented in 2.0 at all (no class, no dispatch entry
+   // anywhere). SESSIONCTL.tag's own <page> definition depends on it
+   // throughout - capturing a tag's own invocation content into a named
+   // variable (<eval name="_BODY"><container></eval>, often with
+   // scope="parent" so a nested custom tag can write back into its
+   // caller's scope: <eval name="AUTHOR" scope="parent">...), and also
+   // using it bare (no name=) to render an <include>'d file's content
+   // inline (<eval><include file="...page"></eval>). Without this tag,
+   // all of that content was silently falling through as undefined-tag
+   // literal text, which is why a real, unmodified SESSIONCTL.tag <page>
+   // never produced its actual rendered body.
+   //
+   // <eval name="X" [scope="local|parent|global"]>content</eval> - same
+   // capture semantics as <set name="X">content</set> (Tag::storeVariable
+   // already implements exactly this: interpret the container, then store
+   // the result - raw if the container itself specified eval="no", already
+   // evaluated otherwise - into variable X at the requested scope,
+   // defaulting to global like <set> does). Reused directly rather than
+   // reimplemented, since it's the identical contract under a different
+   // tag name.
+   //
+   // <eval>content</eval> (no name=) - content is interpreted and flows to
+   // normal output, exactly like any ordinary container-having tag; no
+   // special-casing needed since output/evaluate already default to true
+   // on the base Tag class and the destructor's copyContainer(out,
+   // parentOut) handles the rest once processContainer(container) below
+   // has populated `out`.
+   __eval::__eval(coreutils::ZString &in, coreutils::MString &parentOut, Global &global, Tag *parent, Tag *local) : Tag(in, parentOut, global, parent, local) {
+      if(keywordDefined("name")) {
+	 storeVariable(resolveKeyword("name"));
+	 output = false;
+      } else if(hasContainer) {
+	 processContainer(container);
+      }
+   }
+
+}