fix(qr): accept a one-frame invitation; release v5.9.1

The scanner waited for four frames when shown a single one. Its chunk assembler
was written for SB1, which the generator always cuts into exactly four frames,
and its fallback branch claims any non-JSON string longer than 100 characters —
which a 151-character SBQ2 invitation is. A complete invitation was filed as
chunk 1 of 4, and the scan never finished.

SBQ2 payloads are now recognised as complete before any assembly runs, in both
the text and raw-byte forms, and the hard-coded frame count is marked as
belonging to SB1 so it is not read as a general rule.

src/app.jsx

@@ -4230,6 +4230,30 @@ import {
                         try {
                             console.log('QR Code scanned:', scannedData.substring(0, 100) + '...');
                             console.log('Current buffer state:', qrChunksBufferRef.current);
+
+                            // An SBQ2 invitation is ONE frame, always. It has to be
+                            // recognised before any chunk logic runs: the assembler
+                            // below assumes a fixed four-frame split (that is what
+                            // an SB1 payload is cut into) and the fallback branch
+                            // claims every non-JSON string over 100 characters — a
+                            // 151-character SB2: code matches, is filed as chunk 1
+                            // of 4, and the scanner waits for three frames that do
+                            // not exist.
+                            if (scannedData.startsWith('SB2:') || scannedData.charCodeAt(0) === 0x02) {
+                                qrChunksBufferRef.current = { id: null, total: 0, seen: new Set(), items: [] };
+                                if (showOfferStep) {
+                                    setAnswerInput(scannedData);
+                                } else {
+                                    setOfferInput(scannedData);
+                                }
+                                setMessages(prev => [...prev, {
+                                    message: 'Invitation captured.',
+                                    type: 'success'
+                                }]);
+                                setShowQRScannerModal(false);
+                                return Promise.resolve(true);
+                            }
+
                             
                             // Check if this is a binary chunk (starts with SB1:bin: or is a raw binary chunk)
                             if (scannedData.startsWith('SB1:bin:') || (qrChunksBufferRef.current && qrChunksBufferRef.current.id)) {
@@ -4241,7 +4265,11 @@ import {
                                     // Initialize buffer for binary chunks
                                     qrChunksBufferRef.current = { 
                                         id: `bin_${Date.now()}`, 
-                                        total: 4, // We expect 4 chunks
+                                        // SB1 payloads are split into exactly four
+                                        // frames by the generator above. SBQ2 never
+                                        // reaches here — it is one frame and is
+                                        // handled at the top of this function.
+                                        total: 4,
                                         seen: new Set(), 
                                         items: [],
                                         lastUpdateMs: Date.now()
@@ -4321,7 +4349,11 @@ import {
                                     console.log('Initializing buffer for potential binary chunks');
                                     qrChunksBufferRef.current = { 
                                         id: `bin_${Date.now()}`, 
-                                        total: 4, // We expect 4 chunks
+                                        // SB1 payloads are split into exactly four
+                                        // frames by the generator above. SBQ2 never
+                                        // reaches here — it is one frame and is
+                                        // handled at the top of this function.
+                                        total: 4,
                                         seen: new Set(), 
                                         items: [],
                                         lastUpdateMs: Date.now()