feat(stdlib): Tiled P0 — XML reader + base64 decode + gzip framing (#67)

The three parsing primitives the TMX path needs that were not already in
the tree (zlib inflate + the JSON reader already shipped):

- Xml.* — a minimal, deterministic pure-Ludic XML reader for the
  element/attribute/CDATA subset TMX/TSX/TX use, spliced on demand. Handles
  nested elements, single/double-quoted attributes, text + <![CDATA[…]]>,
  comments, the <?xml?> prolog and <!DOCTYPE>, the five predefined entities
  and numeric character references.
- Base64.* — standard base64 (RFC 4648) decode + a matching pure-Ludic
  encoder; the decoder ignores the whitespace Tiled wraps into <data>.
  Splicing Base64.* also pulls in inflate.ludic so a plain tool can run the
  full base64 -> zlib/gzip decode chain.
- z_gunzip — gzip framing (RFC 1952) over the existing DEFLATE inflater:
  skip the 10-byte header + optional fields, inflate the body, ignore the
  CRC32/ISIZE trailer.

Golden corpus vendored under assets/tiled-fixtures/ (mapeditor/tiled
examples, attributed, + hand-authored multi-encoding fixtures). New
example library/tiled_p0.ludic proves all three (21 assertions); docs
pages + inventory added so check-impl stays green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

changes/tiled-maps.md

@@ -0,0 +1,6 @@
+bump: minor
+type: feat
+
+**Tiled map support (#67–#74)** — load and draw [Tiled](https://www.mapeditor.org/) maps (TMX/TSX/TX and TMJ/TSJ/TJ), the design record from #66.
+
+- **P0 parsing primitives (#67)** — a minimal pure-Ludic XML reader (`Xml.*`) for the element/attribute/CDATA subset TMX/TSX/TX use; standard base64 decode/encode (`Base64.*`, RFC 4648), whose decoder ignores the whitespace Tiled wraps into `<data>`; and gzip framing (`z_gunzip`, RFC 1952) wrapping the existing DEFLATE inflater. zlib and the JSON reader already shipped. A curated, attributed golden corpus lands under `assets/tiled-fixtures/`.