fix(lite): always-populated Console (live status) + single-instance log

The Console could look empty if the wallet produced few events. Make it useful
in every state and remove a cross-platform footgun:

- Add a live status header read straight from the controller (connected /
  connecting / disconnected, sync %, and the last open error) — independent of the
  diagnostics event log, so the Console always shows the current connection +
  wallet-open state even when the log is sparse.
- Move LiteDiagnostics::instance() into a single .cpp so there is exactly one
  instance across the binary, rather than relying on the linker folding an
  inline-function static across translation units (a known fragility, especially
  on mingw/Windows — the most likely cause of a stuck-empty event log there).

Verified the writer and reader share one instance on Linux; builds clean for
full-node, lite, and Windows cross-compile; tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/wallet/lite_diagnostics.h

@@ -24,10 +24,9 @@ namespace wallet {
 
 class LiteDiagnostics {
 public:
-    static LiteDiagnostics& instance() {
-        static LiteDiagnostics inst;
-        return inst;
-    }
+    // Defined in lite_diagnostics.cpp (a single TU) so there is exactly one instance across the
+    // whole binary — no reliance on the linker folding an inline-function static across TUs.
+    static LiteDiagnostics& instance();
 
     // Append a timestamped line (thread-safe). Safe to call from background threads.
     void log(const std::string& message) {