feat: non-blocking warmup — connect during daemon initialization

Instead of blocking the entire UI with "Activating best chain..." until
the daemon finishes warmup, treat warmup responses as a successful
connection. The wallet now:

- Sets connected=true + warming_up=true when daemon returns RPC -28
- Shows warmup status with block progress in the loading overlay
- Polls getinfo every few seconds to detect warmup completion
- Allows Console, Peers, Settings tabs during warmup
- Shows orange status indicator with warmup message in status bar
- Skips balance/tx/address refresh until warmup completes
- Triggers full data refresh once daemon is ready

Also: fix curl handle/header leak on reconnect, fill in empty
externalDetected error branch, bump version to v1.2.0 in build scripts.

src/daemon/embedded_daemon.h

@@ -116,6 +116,26 @@ public:
      * @brief Get last N lines of daemon output (thread-safe snapshot)
      */
     std::vector<std::string> getRecentLines(int maxLines = 8) const;
+
+    /**
+     * @brief Extract the latest block height from daemon output (thread-safe).
+     * Parses the last "height=N" from UpdateTip lines without copying
+     * the entire output buffer.  Returns -1 if no UpdateTip found.
+     */
+    int getLastBlockHeight() const {
+        std::lock_guard<std::mutex> lk(output_mutex_);
+        // Search backwards from the end for "height="
+        size_t pos = process_output_.rfind("height=");
+        if (pos == std::string::npos) return -1;
+        pos += 7; // skip "height="
+        int h = 0;
+        for (size_t i = pos; i < process_output_.size(); ++i) {
+            char c = process_output_[i];
+            if (c >= '0' && c <= '9') h = h * 10 + (c - '0');
+            else break;
+        }
+        return h > 0 ? h : -1;
+    }
     
     /**
      * @brief Whether start() detected an existing daemon on the RPC port.