v0.166.0: mobile nav off-canvas drawer + sidebar cleanup + versioned logo/favicon URLs

Mobile nav was broken — the <=768px block predated the v0.146.0 accordion and
flattened .nav-links into a horizontal overflow-x strip, clipping the accordion's
nested sub-lists. Replaced with a sticky top bar + off-canvas left drawer that
reuses the vertical sidebar (accordion untouched), plus a no-js static fallback.
Removed the sidebar customer-name span (kept on login). Added ?v={{.Version}}
cache-bust to logo/favicon URLs (Cloudflare 4h edge-cache; 0.126.1 failure mode).

Part 4 (outlined-logo constant swap) gated out per §3a: live felhom.eu main still
serves a logo.svg with live <text>/font-family; constants unchanged.

5 new tests via the real layout/CSS render; nav_accordion invariants unchanged.

controller/internal/web/templates/icons.html

@@ -31,4 +31,5 @@
 <symbol id="i-chevron-down" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="m6 9 6 6 6-6" /></symbol>
 <symbol id="i-play" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M5 5a2 2 0 0 1 3.008-1.728l11.997 6.998a2 2 0 0 1 .003 3.458l-12 7A2 2 0 0 1 5 19z" /></symbol>
 <symbol id="i-pause" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><rect x="14" y="3" width="5" height="18" rx="1" /> <rect x="5" y="3" width="5" height="18" rx="1" /></symbol>
+<symbol id="i-menu" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M4 12h16" /> <path d="M4 6h16" /> <path d="M4 18h16" /></symbol>
 </svg>{{end}}