Disable implicit_figures in all Pandoc calls to suppress image captions

Unify Pandoc input format to markdown-implicit_figures across docx export,
pptx slide preview, and MCP fallback. This prevents alt text from appearing
as italic captions below images. Remove the now-unnecessary figcaption
stripping regex from SlideService.

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

Author: yotsuda

MarkdownPointer.Mcp/Tools/MarkdownPointerTools.cs

@@ -237,7 +237,7 @@ public async Task<string> ExportDocument(
                 StartInfo = new ProcessStartInfo
                 {
                     FileName = "pandoc",
-                    Arguments = $"-f markdown -t docx {refDoc}-o \"{outputPath}\" \"{fullPath}\"",
+                    Arguments = $"-f markdown-implicit_figures -t docx {refDoc}-o \"{outputPath}\" \"{fullPath}\"",
                     UseShellExecute = false,
                     CreateNoWindow = true,
                     RedirectStandardError = true

MarkdownPointer/Services/PandocService.cs

@@ -35,7 +35,7 @@ public static class PandocService
                     StartInfo = new ProcessStartInfo
                     {
                         FileName = "pandoc",
-                        Arguments = $"-f markdown -t {format} {refDoc}{resPath}-o \"{outputPath}\" \"{markdownPath}\"",
+                        Arguments = $"-f markdown-implicit_figures -t {format} {refDoc}{resPath}-o \"{outputPath}\" \"{markdownPath}\"",
                         UseShellExecute = false,
                         CreateNoWindow = true,
                         RedirectStandardError = true

MarkdownPointer/Services/SlideService.cs

@@ -33,8 +33,6 @@ public static class SlideService
 
             // Pandoc uses data-src for lazy loading in reveal.js; convert to src for WebView2
             html = html.Replace("data-src=\"", "src=\"");
-            // Remove figcaption elements (Pandoc wraps images in <figure> with alt text as caption)
-            html = Regex.Replace(html, @"<figcaption[^>]*>.*?</figcaption>", "", RegexOptions.Singleline);
 
             // Inline local images as base64 (NavigateToString blocks file:// access)
             var baseDir = Path.GetDirectoryName(markdownPath)!;
@@ -82,7 +80,7 @@ public static class SlideService
                     var psi = new ProcessStartInfo
                     {
                         FileName = "pandoc",
-                        Arguments = $"-f markdown -t revealjs -s " +
+                        Arguments = $"-f markdown-implicit_figures -t revealjs -s " +
                                     $"--variable revealjs-url=https://cdn.jsdelivr.net/npm/reveal.js@5.2.1 " +
                                     $"--variable theme={theme} " +
                                     $"-o \"{outputPath}\" \"{markdownPath}\"",