fix: separate reachability check from version detection in get-lnbits-key.sh

The script used /api/v1/health for both reachability testing and version
detection. Since that endpoint only exists on LNbits 0.12+, old versions
were incorrectly reported as "not reachable" instead of falling through
to the legacy superuser API path.

Now the script:
- Tests reachability via GET / (works on all LNbits versions)
- Uses /api/v1/health only for version detection
- If health endpoint is absent, correctly assumes pre-0.12 (legacy path)
- If health endpoint exists but lacks server_version, assumes 0.12+

Fixes #19

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/bitcoin-ln-node/get-lnbits-key.sh

@@ -67,9 +67,15 @@ print_export_template() {
 # ─── Step 1: Confirm LNbits is reachable ─────────────────────────────────────
 
 info "Checking LNbits at $LNBITS_LOCAL …"
-HEALTH_JSON="$(curl -sf --max-time 6 "$LNBITS_LOCAL/api/v1/health" 2>/dev/null || true)"
 
-if [[ -z "$HEALTH_JSON" ]]; then
+# Use a plain GET to the root URL to test reachability (works on all versions).
+# The health endpoint (/api/v1/health) only exists on 0.12+.
+LNBITS_REACHABLE=false
+if curl -sf --max-time 6 -o /dev/null "$LNBITS_LOCAL/" 2>/dev/null; then
+  LNBITS_REACHABLE=true
+fi
+
+if [[ "$LNBITS_REACHABLE" != "true" ]]; then
   warn "LNbits is not reachable at $LNBITS_LOCAL (is it running?)."
   warn "Showing manual setup instructions — run this script again once LNbits is up."
   echo ""
@@ -80,18 +86,30 @@ if [[ -z "$HEALTH_JSON" ]]; then
   exit 0
 fi
 
+ok "LNbits is reachable at $LNBITS_LOCAL"
+
 # ─── Step 2: Detect LNbits version ───────────────────────────────────────────
 
+# Try the health endpoint (available on 0.12+) to get the server version.
+HEALTH_JSON="$(curl -sf --max-time 6 "$LNBITS_LOCAL/api/v1/health" 2>/dev/null || true)"
+
 LNBITS_VERSION=""
-if command -v python3 &>/dev/null; then
+if [[ -n "$HEALTH_JSON" ]] && command -v python3 &>/dev/null; then
   LNBITS_VERSION="$(echo "$HEALTH_JSON" \
     | python3 -c "import sys,json; d=json.load(sys.stdin); print(d.get('server_version',''))" \
     2>/dev/null || true)"
 fi
 
 if [[ -z "$LNBITS_VERSION" ]]; then
-  warn "Could not parse server_version from health endpoint — assuming modern LNbits (>= 0.12)."
+  if [[ -z "$HEALTH_JSON" ]]; then
-  LNBITS_VERSION="0.12.0"
+    # Health endpoint not found — this is a pre-0.12 LNbits that lacks /api/v1/health.
+    warn "Health endpoint not available — assuming legacy LNbits (< 0.12)."
+    LNBITS_VERSION="0.11.0"
+  else
+    # Health endpoint responded but didn't include server_version.
+    warn "Could not parse server_version from health endpoint — assuming modern LNbits (>= 0.12)."
+    LNBITS_VERSION="0.12.0"
+  fi
 fi
 
 info "LNbits version: ${LNBITS_VERSION}"