feat: Make METARs sharable via URL hash

Co-authored-by: aider (gemini/gemini-2.5-pro) <aider@aider.chat>

metar.html

@@ -806,15 +806,23 @@
             return sections;
         }
 
-        function displayNewMetar() {
+        function displayMetar(index) {
             if (metars.length === 0) {
                 metarDisplay.textContent = 'No METARs loaded.';
                 return;
             }
-            // Bias random selection towards the more interesting (higher-scored) METARs at the start of the array.
-            // Math.random() * Math.random() skews distribution towards 0.
-            const randomIndex = Math.floor(Math.random() * Math.random() * metars.length);
-            const metarString = metars[randomIndex].metar;
+
+            let metarIndex;
+            if (index !== undefined && index >= 0 && index < metars.length) {
+                metarIndex = index;
+            } else {
+                // Bias random selection towards the more interesting (higher-scored) METARs at the start of the array.
+                // Math.random() * Math.random() skews distribution towards 0.
+                metarIndex = Math.floor(Math.random() * Math.random() * metars.length);
+            }
+
+            const metarString = metars[metarIndex].metar;
+            window.location.hash = metarIndex;
 
             currentMetarSections = generateMetarSections(metarString);
             currentSectionIndex = 0;
@@ -861,14 +869,21 @@
                     console.log(`  - Score: ${metars[i].score.toFixed(2)}, METAR: ${metars[i].metar}`);
                 }
 
-                displayNewMetar(); // Display initial METAR
+                const hash = window.location.hash.substring(1);
+                const initialIndex = parseInt(hash, 10);
+
+                if (!isNaN(initialIndex) && initialIndex >= 0 && initialIndex < metars.length) {
+                    displayMetar(initialIndex);
+                } else {
+                    displayMetar(); // Display initial random METAR
+                }
             })
             .catch(error => {
                 console.error('Error fetching or parsing metars.txt:', error)
                 metarDisplay.textContent = 'Could not load METARs.';
             });
 
-        newMetarBtn.addEventListener('click', displayNewMetar);
+        newMetarBtn.addEventListener('click', () => displayMetar());
         decodeAllCheckbox.addEventListener('change', updateDisplay);
 
         function updateDisplay() {