refactor: replace inline frontmatter code with frontmatter package

Removed ~60 lines of inline frontmatter parsing (FMState, Frontmatter,
ParseResult types, fmFoldLine, parseFrontmatter, and accessor functions).
Now uses the frontmatter package via import.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

main.lux

@@ -1,20 +1,12 @@
 import markdown
+import frontmatter
 
 type SiteConfig =
     | SiteConfig(String, String, String, String, String, String, String)
 
-type Frontmatter =
-    | Frontmatter(String, String, String, String)
-
-type ParseResult =
-    | ParseResult(Frontmatter, String)
-
 type Page =
     | Page(String, String, String, String, String)
 
-type FMState =
-    | FMState(Bool, Bool, String, String, String, String, String)
-
 type TagEntry =
     | TagEntry(String, String, String, String, String)
 
@@ -103,49 +95,6 @@ fn cfgStaticDir(c: SiteConfig): String =
     SiteConfig(_, _, _, _, _, _, sd) => sd,
 }
 
-fn fmFoldLine(acc: FMState, line: String): FMState =
-    match acc {
-    FMState(inFront, pastFront, title, date, desc, tags, body) => if pastFront then FMState(inFront, pastFront, title, date, desc, tags, body + line + "
-") else if String.trim(line) == "---" then if inFront then FMState(false, true, title, date, desc, tags, body) else FMState(true, false, title, date, desc, tags, body) else if inFront then match String.indexOf(line, ": ") {
-    Some(idx) => {
-    let key = String.trim(String.substring(line, 0, idx))
-    let rawVal = String.trim(String.substring(line, idx + 2, String.length(line)))
-    let val = if String.startsWith(rawVal, "\"") then String.substring(rawVal, 1, String.length(rawVal) - 1) else rawVal
-    if key == "title" then FMState(inFront, pastFront, val, date, desc, tags, body) else if key == "date" then FMState(inFront, pastFront, title, val, desc, tags, body) else if key == "description" then FMState(inFront, pastFront, title, date, val, tags, body) else if key == "tags" then FMState(inFront, pastFront, title, date, desc, val, body) else acc
-},
-    None => acc,
-} else acc,
-}
-
-fn parseFrontmatter(content: String): ParseResult = {
-    let lines = String.lines(content)
-    let init = FMState(false, false, "", "", "", "", "")
-    let result = List.fold(lines, init, fmFoldLine)
-    match result {
-    FMState(_, _, title, date, desc, tags, body) => ParseResult(Frontmatter(title, date, desc, tags), body),
-}
-}
-
-fn fmTitle(f: Frontmatter): String =
-    match f {
-    Frontmatter(t, _, _, _) => t,
-}
-
-fn fmDate(f: Frontmatter): String =
-    match f {
-    Frontmatter(_, d, _, _) => d,
-}
-
-fn fmTagsRaw(f: Frontmatter): String =
-    match f {
-    Frontmatter(_, _, _, t) => t,
-}
-
-fn fmTags(f: Frontmatter): List<String> =
-    match f {
-    Frontmatter(_, _, _, t) => if t == "" then [] else String.split(t, " "),
-}
-
 fn pgDate(p: Page): String =
     match p {
     Page(d, _, _, _, _) => d,
@@ -262,18 +211,15 @@ fn htmlTagPage(tagName: String, postsHtml: String): String = "<div class=\"page
 
 fn parseFile(path: String): Page with {File} = {
     let raw = File.read(path)
-    let parsed = parseFrontmatter(raw)
-    match parsed {
-    ParseResult(front, body) => {
-    let title = fmTitle(front)
-    let date = fmDate(front)
-    let tags = fmTagsRaw(front)
+    let doc = frontmatter.parse(raw)
+    let title = frontmatter.title(doc)
+    let date = frontmatter.date(doc)
+    let tags = frontmatter.getOrDefault(doc, "tags", "")
+    let body = frontmatter.body(doc)
     let htmlContent = convertMd(body)
     let filename = basename(path)
     let slug = slugFromFilename(filename)
     Page(date, title, slug, tags, htmlContent)
-},
-}
 }
 
 fn mapParseFiles(dir: String, files: List<String>): List<Page> with {File} =
@@ -384,10 +330,8 @@ fn writeTagPages(outputDir: String, allTagEntries: List<TagEntry>, siteTitle: St
 
 fn renderSnippetFile(snippetDir: String, filename: String): String with {File} = {
     let raw = File.read(snippetDir + "/" + filename)
-    let parsed = parseFrontmatter(raw)
-    match parsed {
-    ParseResult(_, body) => htmlSnippetCard(convertMd(body)),
-}
+    let doc = frontmatter.parse(raw)
+    htmlSnippetCard(convertMd(frontmatter.body(doc)))
 }
 
 fn renderSnippets(snippetDir: String, files: List<String>): List<String> with {File} =