Add frontmatter, markdown, path, xml, rss, and web packages

Sync local packages into the registry repo and update index.json
and README.md to include all 9 packages.

packages/frontmatter/test_snapshot.lux

@@ -0,0 +1,79 @@
+import lib
+
+// Snapshot tests: verify complete parse output against golden values
+
+// Snapshot: full blog post parse
+fn test_snapshot_blog_post(): Unit with {Test} = {
+    let input = "---\ntitle: Understanding Algebraic Effects\ndate: 2025-03-15\ndescription: A deep dive into effect systems\ntags: lux effects programming\nauthor: Brandon\nlayout: post\n---\n# Understanding Algebraic Effects\n\nAlgebraic effects are a powerful way to handle side effects.\n\n## What are they?\n\nThey let you declare what effects your code uses."
+    let doc = lib.parse(input)
+    Test.assertEqualMsg("Understanding Algebraic Effects", lib.title(doc), "snap: title")
+    Test.assertEqualMsg("2025-03-15", lib.date(doc), "snap: date")
+    Test.assertEqualMsg("A deep dive into effect systems", lib.description(doc), "snap: description")
+    Test.assertEqualMsg(3, List.length(lib.tags(doc)), "snap: tag count")
+    Test.assertEqualMsg("Brandon", lib.getOrDefault(doc, "author", ""), "snap: author")
+    Test.assertEqualMsg("post", lib.getOrDefault(doc, "layout", ""), "snap: layout")
+    Test.assertEqualMsg(6, List.length(lib.entries(doc)), "snap: entry count")
+    Test.assert(String.startsWith(lib.body(doc), "# Understanding"), "snap: body starts with heading")
+    Test.assert(String.contains(lib.body(doc), "## What are they?"), "snap: body contains subheading")
+}
+
+// Snapshot: minimal frontmatter
+fn test_snapshot_minimal(): Unit with {Test} = {
+    let input = "---\ntitle: Hello\n---\nWorld"
+    let doc = lib.parse(input)
+    Test.assertEqualMsg("Hello", lib.title(doc), "snap: minimal title")
+    Test.assertEqualMsg("", lib.date(doc), "snap: minimal no date")
+    Test.assertEqualMsg("", lib.description(doc), "snap: minimal no description")
+    Test.assertEqualMsg(0, List.length(lib.tags(doc)), "snap: minimal no tags")
+    Test.assertEqualMsg(1, List.length(lib.entries(doc)), "snap: minimal one entry")
+    Test.assert(String.startsWith(lib.body(doc), "World"), "snap: minimal body")
+}
+
+// Snapshot: no frontmatter at all
+fn test_snapshot_no_frontmatter(): Unit with {Test} = {
+    let input = "This is just plain text.\nNo frontmatter here."
+    let doc = lib.parse(input)
+    Test.assertEqualMsg(false, lib.hasFrontmatter(doc), "snap: no frontmatter")
+    Test.assertEqualMsg("", lib.title(doc), "snap: no fm title")
+    Test.assertEqualMsg("", lib.date(doc), "snap: no fm date")
+    Test.assertEqualMsg(0, List.length(lib.entries(doc)), "snap: no fm entries")
+}
+
+// Snapshot: quoted values with various quote styles
+fn test_snapshot_quoted_values(): Unit with {Test} = {
+    let input = "---\ntitle: \"Double Quoted: Title\"\nsubtitle: 'Single Quoted: Subtitle'\nplain: Just a plain value\n---\nBody"
+    let doc = lib.parse(input)
+    Test.assertEqualMsg("Double Quoted: Title", lib.title(doc), "snap: double-quoted")
+    Test.assertEqualMsg("Single Quoted: Subtitle", lib.getOrDefault(doc, "subtitle", ""), "snap: single-quoted")
+    Test.assertEqualMsg("Just a plain value", lib.getOrDefault(doc, "plain", ""), "snap: unquoted")
+}
+
+// Snapshot: document with many entries
+fn test_snapshot_many_entries(): Unit with {Test} = {
+    let input = "---\ntitle: Complex Post\ndate: 2025-06-01\ndescription: A complex post\ntags: a b c d e\nauthor: Alice\nlayout: page\ncategory: tech\nslug: complex-post\ndraft: false\nweight: 42\n---\nBody content here."
+    let doc = lib.parse(input)
+    Test.assertEqualMsg(10, List.length(lib.entries(doc)), "snap: ten entries")
+    Test.assertEqualMsg("Complex Post", lib.title(doc), "snap: title")
+    Test.assertEqualMsg("2025-06-01", lib.date(doc), "snap: date")
+    Test.assertEqualMsg(5, List.length(lib.tags(doc)), "snap: five tags")
+    Test.assertEqualMsg("Alice", lib.getOrDefault(doc, "author", ""), "snap: author")
+    Test.assertEqualMsg("page", lib.getOrDefault(doc, "layout", ""), "snap: layout")
+    Test.assertEqualMsg("tech", lib.getOrDefault(doc, "category", ""), "snap: category")
+    Test.assertEqualMsg("complex-post", lib.getOrDefault(doc, "slug", ""), "snap: slug")
+    Test.assertEqualMsg("false", lib.getOrDefault(doc, "draft", ""), "snap: draft")
+    Test.assertEqualMsg("42", lib.getOrDefault(doc, "weight", ""), "snap: weight")
+}
+
+// Snapshot: entry iteration order
+fn test_snapshot_entry_order(): Unit with {Test} = {
+    let input = "---\nfirst: 1\nsecond: 2\nthird: 3\n---\n"
+    let doc = lib.parse(input)
+    let es = lib.entries(doc)
+    match List.head(es) {
+        Some(e) => {
+            Test.assertEqualMsg("first", lib.entryKey(e), "snap: first entry key")
+            Test.assertEqualMsg("1", lib.entryValue(e), "snap: first entry value")
+        },
+        None => Test.assert(false, "snap: should have entries"),
+    }
+}