chore: stage I1 -- repo cleanup, minimal README

Working plans (docs/development, docs/design redesign notes) removed; the
two developer guides moved to docs/developer/. README cut to devices,
flashing, links and building (Wio Tracker L2 added); its feature list and
doc tables moved to docs/solo_features/README.md. RELEASE.md describes the
Solo release flow. Upstream's GitHub Pages workflow (docs.meshcore.io)
dropped, CLAUDE.md untracked, Buy Me a Coffee back in FUNDING.yml.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/companion_radio/ui-lvgl/UITask.cpp

@@ -95,7 +95,7 @@ static const char* waypointsFull() {
   return t;
 }
 
-// ui-lvgl skeleton (docs/development/ui-core.md, step 5): status bar, home,
+// ui-lvgl skeleton (docs/developer/ui-core.md, step 5): status bar, home,
 // conversation list, contact picker, conversation view with compose. Every
 // piece of state it shows comes from the UI Core; this file only draws it.
 
@@ -990,8 +990,7 @@ void UITask::loop() {
   prefsFlush();
   usbPoll();
 #if defined(UI_HEAP_REPORT) && defined(ESP32)
-  // -D UI_HEAP_REPORT: internal / PSRAM heap once, 20 s after boot (the
-  // framework comparison in docs/development/l2-roadmap.md).
+  // -D UI_HEAP_REPORT: internal / PSRAM heap once, 20 s after boot.
   static bool heap_done = false;
   if (!heap_done && millis() > 20000) {
     heap_done = true;