Add hover provider for YAML editor

Introduces a hover provider to the YAML editor using Monaco, displaying property descriptions from the schema when hovering over keys. This enhances the editor's usability by providing inline documentation for YAML properties.

www/config.html

@@ -770,6 +770,7 @@
 
         let schemaTools = null;
         let completionProvider = null;
+        let hoverProvider = null;
 
         const scheduleLint = (() => {
             let handle = null;
@@ -932,6 +933,69 @@
                     return {suggestions};
                 }
             });
+
+            if (hoverProvider) hoverProvider.dispose();
+            hoverProvider = monaco.languages.registerHoverProvider('yaml', {
+                provideHover: (model, position) => {
+                    if (!schemaTools) return null;
+
+                    const line = model.getLineContent(position.lineNumber);
+                    const lineNoComment = stripInlineComment(line).trimEnd();
+                    const listItem = parseListItem(lineNoComment);
+
+                    const cursorIndex = position.column - 1;
+                    if (listItem && cursorIndex < listItem.afterDashIndex) return null;
+
+                    let kv;
+                    let effectiveIndent;
+                    let keyStartIndex;
+                    let keyEndIndex;
+
+                    if (listItem) {
+                        if (!listItem.rest) return null;
+                        const synthetic = ' '.repeat(listItem.contentIndent) + listItem.rest;
+                        kv = parseKey(synthetic);
+                        if (!kv) return null;
+                        effectiveIndent = listItem.contentIndent;
+                        keyStartIndex = listItem.afterDashIndex + (kv.keyStartIndex - listItem.contentIndent);
+                        keyEndIndex = listItem.afterDashIndex + (kv.keyEndIndex - listItem.contentIndent);
+                    } else {
+                        kv = parseKey(lineNoComment);
+                        if (!kv) return null;
+                        effectiveIndent = countIndent(lineNoComment);
+                        keyStartIndex = kv.keyStartIndex;
+                        keyEndIndex = kv.keyEndIndex;
+                    }
+
+                    if (cursorIndex < keyStartIndex || cursorIndex >= keyEndIndex) return null;
+
+                    const stack = buildContextStack(model, position.lineNumber - 1);
+                    while (stack.length > 1 && effectiveIndent <= stack[stack.length - 1].indent) stack.pop();
+
+                    let contextSchema = resolveRef(stack[stack.length - 1].schema);
+                    if (listItem && cursorIndex >= listItem.afterDashIndex && contextSchema && contextSchema.type === 'array') {
+                        contextSchema = resolveRef(contextSchema.items);
+                    }
+
+                    if (!contextSchema) return null;
+                    const propSchema = getPropertySchema(contextSchema, kv.key);
+                    if (!propSchema) return null;
+
+                    const resolved = resolveRef(propSchema);
+                    const description = resolved?.description;
+                    if (!description) return null;
+
+                    return {
+                        range: new monaco.Range(
+                            position.lineNumber,
+                            keyStartIndex + 1,
+                            position.lineNumber,
+                            keyEndIndex + 1
+                        ),
+                        contents: [{value: description}],
+                    };
+                }
+            });
         };
 
         let dump;