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/index.ex

@@ -29,7 +29,8 @@ defmodule OrgGarden.Index do
             path
             |> File.read!()
             |> then(fn content ->
-              case Regex.run(~r/^title\s*=\s*"(.+)"/m, content) do
+              # Match YAML frontmatter: title: "value" or title: value
+              case Regex.run(~r/^title:\s*"?(.+?)"?\s*$/m, content) do
                 [_, t] -> t
                 _ -> slug
               end
@@ -76,8 +77,8 @@ defmodule OrgGarden.Index do
 
   defp generated_index?(content) do
     # Our generated index uses "title: Index" in YAML frontmatter.
-    # ox-hugo uses TOML frontmatter (title = "..."), so this won't
-    # match user-exported files.
+    # ox-hugo also uses YAML frontmatter now, so we check for our specific
+    # title to distinguish generated vs user-exported index files.
     String.contains?(content, "title: Index")
   end
 end