Add piano-mode help viewer bound to question mark

client/public/help.json

@@ -87,7 +87,7 @@
         },
         {
           "keys": "Piano mode",
-          "description": "When using a piano: 1-9 (and 0 for the 10th slot) changes instrument, -/= changes octave, ASDFGHJKL;' plays C major notes, WETYUOP] plays sharps, Z starts/stops recording, X plays recording, C stops playback, Escape exits"
+          "description": "When using a piano: press question mark for piano help. 1-9 (and 0 for the 10th slot) changes instrument, -/= changes octave, ASDFGHJKL;' plays C major notes, WETYUOP] plays sharps, Z starts/stops recording, X plays recording, C stops playback, Escape exits"
         }
       ]
     },

client/public/piano.json

@@ -0,0 +1,41 @@
+{
+  "sections": [
+    {
+      "title": "Piano Mode",
+      "items": [
+        {
+          "keys": "A S D F G H J K L ; '",
+          "description": "Play white keys (C major scale from C4)."
+        },
+        {
+          "keys": "W E T Y U O P ]",
+          "description": "Play sharp keys."
+        },
+        {
+          "keys": "1-9, 0",
+          "description": "Change instrument presets."
+        },
+        {
+          "keys": "- / =",
+          "description": "Shift octave down or up."
+        },
+        {
+          "keys": "Z",
+          "description": "Start or stop recording (up to 30 seconds)."
+        },
+        {
+          "keys": "X",
+          "description": "Play the saved recording."
+        },
+        {
+          "keys": "C",
+          "description": "Stop recording playback."
+        },
+        {
+          "keys": "Escape",
+          "description": "Exit piano mode."
+        }
+      ]
+    }
+  ]
+}

client/public/version.js

@@ -1,5 +1,5 @@
 // Maintainer-controlled web client version.
 // Format: YYYY.MM.DD Rn (example: 2026.02.20 R2)
-window.CHGRID_WEB_VERSION = "2026.02.22 R208";
+window.CHGRID_WEB_VERSION = "2026.02.22 R209";
 // Optional display timezone for timestamps. Falls back to America/Detroit if unset/invalid.
 window.CHGRID_TIME_ZONE = "America/Detroit";