Add WML renderer for WAP decks

Adds a `wml` renderer plugin converting Markdown into WML decks for
old WAP browsers, following the existing parser -> BlockEvent stream
-> renderer plugin architecture (see gemini/micron/ama renderers).

WML content is idiomatically short and button/link-navigated rather
than one long page, so unlike the other renderers, `wml` can split a
document into multiple <card>s -- but only opt-in:

- Manual `{.card}` / `{.card Title}` divider directives (new,
  format-agnostic BlockKind.CARD_BREAK; silently ignored by every
  other renderer via their existing unhandled-kind no-op path).
- Heading-level splitting via `--renderer-option split_level=N`,
  ignored when manual dividers are present.
- Plain documents with neither stay a single card (the safe default).

When a document resolves to 2+ cards, a hub-and-spoke menu card is
built by default (button/link choices -> section, Back to menu), or
`menu=false` switches to a linear Next/Back chain. A byte-overflow
safety net (`max_card_bytes`, default 1400) paginates any single
section that's still too large.

Also adds GFM pipe-table support (BlockKind.TABLE) via the same
sentinel-injection preprocessing trick already used for ASCII art
blocks, so the parser's line-by-line loop needed no lookahead rework.
Rendered as `<table>` in wml, silently ignored elsewhere.

No new dependencies. No devbox/jj/test-suite additions -- decided
against for this repo (see README for the full option reference).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

examples/wml-manual.md

@@ -0,0 +1,14 @@
+Live updates for the ridge trail network. Reception is spotty past the tree line, check before you go.
+
+{.card Weather}
+Cold and clear. Wind: **15 mph** gusting from the *northwest*. Permit fee: $5.
+
+{.card Trail Status}
+- North Loop: open
+- South Loop: closed
+- Summit Spur: open, ice above 2000m
+
+{.card Contact}
+Ranger station: [call dispatch](tel:+15555550123)
+
+![Trail map](https://example.com/map.png)