v1.9.18: SMS concatenation — incoming reassembly + outgoing limit

Incoming: _parse_sms_concat parses UDH for IEI 0x00 (8-bit ref) and
IEI 0x08 (16-bit ref). PoRSubmitHandler accumulates segments, sorts by
num, and reassembles complete payload when all parts arrive.

Outgoing: MAX_ENVELOPE_SEGMENTS=5 limits the secured packet to 5
ENVELOPE chunks (650B max at 130B/chunk).

10 new tests for concat parsing and reassembly.

frontend/index.html

@@ -18,7 +18,7 @@
 <div class="max-w-7xl mx-auto px-6 py-2">
 
 	<div class="flex items-center justify-between mb-3">
-		<h1 class="text-2xl font-bold text-heading">OTAMan <span id="slogan" class="text-sm font-normal text-gray-500 dark:text-slate-400 ml-2" data-l10n="SIM OTA with a Human Face">SIM OTA with a Human Face</span> <span class="text-xs text-gray-400 dark:text-slate-500 ml-1">v1.9.17</span></h1>
+		<h1 class="text-2xl font-bold text-heading">OTAMan <span id="slogan" class="text-sm font-normal text-gray-500 dark:text-slate-400 ml-2" data-l10n="SIM OTA with a Human Face">SIM OTA with a Human Face</span> <span class="text-xs text-gray-400 dark:text-slate-500 ml-1">v1.9.18</span></h1>
 		<div class="flex items-center gap-4">
 			<button id="install-btn" class="px-2 py-1 text-xs rounded border border-gray-300 dark:border-slate-600 hover:bg-gray-200 dark:hover:bg-slate-700" style="display:none">INSTALL PWA [for offline use]</button>
 			<a href="https://github.com/anttro/otaman" target="_blank" class="text-xs text-gray-400 hover:text-gray-600 dark:text-slate-500 dark:hover:text-slate-300">github</a>

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'otaman-v29';
+const CACHE = 'otaman-v30';
 const URLS = [
   'index.html',
   'help.html',