Switch ox-hugo export from TOML to YAML frontmatter

TOML frontmatter interprets bare dates like 2022-10-31 as date literals
requiring time components, causing parsing issues. YAML handles dates
as strings by default, avoiding these problems.

Changes:
- export.ex: Add org-hugo-front-matter-format set to yaml
- index.ex: Update title regex to match YAML format (title: vs title =)
- quartz.config.ts: Use default FrontMatter plugin (YAML) instead of TOML

quartz-config/quartz.config.ts

@@ -55,7 +55,7 @@ const config: QuartzConfig = {
   },
   plugins: {
     transformers: [
-      Plugin.FrontMatter({ delimiters: "+++", language: "toml" }),
+      Plugin.FrontMatter(),
       Plugin.CreatedModifiedDate({
         priority: ["frontmatter", "git", "filesystem"],
       }),
@@ -68,8 +68,6 @@ const config: QuartzConfig = {
       }),
       // OxHugoFlavouredMarkdown must come before GitHubFlavoredMarkdown.
       // Note: not compatible with ObsidianFlavoredMarkdown — use one or the other.
-      // If ox-hugo exports TOML frontmatter, change FrontMatter to:
-      //   Plugin.FrontMatter({ delims: "+++", language: "toml" })
       Plugin.OxHugoFlavouredMarkdown(),
       Plugin.GitHubFlavoredMarkdown(),
       Plugin.TableOfContents(),