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

lib/org_garden/export.ex

@@ -73,6 +73,9 @@ defmodule OrgGarden.Export do
                   (format "[cite:%s]" (string-join keys ";")))))
             """,
             "--eval", "(setq org-cite-export-processors '((t passthrough)))",
+            # Use YAML frontmatter instead of TOML to avoid date parsing issues
+            # (TOML interprets bare dates like 2022-10-31 as date literals requiring time)
+            "--eval", "(setq org-hugo-front-matter-format 'yaml)",
             "--eval", ~s[(setq org-hugo-base-dir "#{output_dir}")],
             "--eval", ~s[(setq org-hugo-default-section-directory "#{section}")],
             "--visit", orgfile,