Extract the WML exporter from md2txt into wapdown

md2txt is a suite of minimal text-based markup exporters, and every other
renderer in it (text, micron, ama, gemini, nex) is a straight transform of
a document into a flat text format. The WML renderer is neither: it emits
an XML tree, and it restructures the document rather than transforming it
-- splitting one file into many <card>s, inventing navigation between
them, building a menu card that exists in no source document, and
paginating on a byte budget. That is why it needed levers no sibling
renderer needed, and why it alone forced a CARD_BREAK block kind and a
{.card} directive into the shared parser that every other renderer
ignores.

wapdown is that renderer given a repository of its own, where
restructuring a document into a navigable deck is the point.

Ported: the Markdown parser, block event models, and pipeline core, each
trimmed to what a deck compiler actually uses (no FIGlet, no hyphenation,
no ASCII-art includes, no text-layout frontmatter), plus the eight inline
regexes the renderer had been borrowing from a 1039-line text renderer.
The plugin registry comes along so other WAP-era targets can register
alongside wml later. Zero runtime dependencies.

Config is now first-class: every lever is an argparse flag with
validation and a frontmatter equivalent, layered CLI > frontmatter >
default, replacing the generic --renderer-option KEY=VALUE passthrough.

Five defects found while reading the code, each with a regression test:

- Link and image URLs were shredded by the emphasis patterns, which ran
  before LINK_RE: a path like /v1_2_3/ became /v1<i>2</i>3/ inside the
  href. Links and images are now resolved and stashed first.
- <table> was emitted as a direct child of <card>. The WML 1.3 content
  model is (onevent*, timer?, (do | p | pre)*), so it must sit in a <p>.
- Link labels carried emphasis, but <a> is declared (#PCDATA | br | img)*
  -- there is nowhere valid for a <b> inside one. Markers are now stripped.
- The menu card was built directly and never byte-packed, so the one card
  most likely to be large was the one card exempt from the budget.
- Output was written with CRLF line endings. WML is XML served over HTTP.

New, WAP-idiomatic rather than Markdown-idiomatic:

- deck-level <template> hoisting nav that would otherwise repeat per card
- <select> menus, picked with a keypad digit instead of scrolled to
- --deck-per-card, one file per section cross-linked by filename, which
  is the real answer to per-deck cache limits
- <head> metadata: Cache-Control max-age and <access>
- a Home options softkey, which <prev/> alone cannot provide
- an image policy (keep/alt/drop) for the WBMP-only reality of WAP 1.x
  browsers -- no conversion is performed

186 tests, where neither repo had any. Golden files pin whole-document
output; every deck is validated against the real WML 1.3 DTD, vendored at
tests/dtd/wml13.dtd. Rendering examples/trail.md still matches md2txt's
committed output byte for byte, modulo the CRLF fix.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/regenerate_golden.py

@@ -0,0 +1,44 @@
+#!/usr/bin/env python3
+"""Rewrite every golden file under tests/golden/.
+
+Run after an intentional change to the renderer, then read the diff --
+that diff is the change, stated in output rather than in code:
+
+    uv run python tests/regenerate_golden.py
+    jj diff tests/golden
+"""
+from __future__ import annotations
+
+import shutil
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parent))
+
+from conftest import EXAMPLES, GOLDEN, render_file  # noqa: E402
+from golden_cases import CASES, MULTI_CASES  # noqa: E402
+
+
+def main() -> int:
+    GOLDEN.mkdir(parents=True, exist_ok=True)
+
+    for name, (source, options) in CASES.items():
+        output = render_file(EXAMPLES / source, **options)
+        (GOLDEN / f"{name}.wml").write_text(output.text, encoding="utf-8")
+        print(f"wrote {name}.wml")
+
+    for name, (source, options) in MULTI_CASES.items():
+        directory = GOLDEN / name
+        if directory.exists():
+            shutil.rmtree(directory)
+        directory.mkdir(parents=True)
+        for document in render_file(EXAMPLES / source, **options).documents:
+            (directory / (document.name or "index.wml")).write_text(
+                document.text, encoding="utf-8"
+            )
+        print(f"wrote {name}/ ({len(list(directory.iterdir()))} files)")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())