phase 4: vimwiki parser + SyntaxPlugin glue

Hand-rolled recursive-descent parser over the token stream. Resilient
per SPEC §6.7: never aborts the document — anything the dispatcher
can't claim becomes BlockNode::Error and the cursor advances, and
unterminated wikilinks / transclusions / delimiters fall back to
literal text.

Block coverage: every variant from §6.4 — Heading (with inline
content between markers), Paragraph (with soft-break across single
newlines), HorizontalRule, Blockquote (both `>` and 4-space styles),
Preformatted, MathBlock, List (with checkbox + indent-driven
sublists), DefinitionList, Table (header separator promotes the
preceding row, plus colspan / rowspan cells), Comment (single +
multiline), and page-level placeholders threaded into PageMetadata.

Inline pairing: left-to-right scan with "find next matching delim",
recursing on the slice between. `_*x*_` becomes Italic(Bold(...)),
mirroring SPEC §6.7 precedence. URLs inside `[[ ]]` route to
ExternalLinkNode; everything else to WikiLinkNode with full
LinkTarget classification (Wiki / Interwiki numbered + named /
Diary / File / Local / AnchorOnly / directory / root-relative /
filesystem-absolute).

VimwikiSyntax registers as id="vimwiki", extensions=[".wiki"] and
chains lexer + parser inside SyntaxPlugin::parse.

SPEC §4 updated to record the hand-rolled choice with rationale —
span-bearing tokens fit awkwardly into winnow/nom combinator style;
resilience and recovery are explicit in code instead.

Tests (41 new parser cases) cover every AST construct, inline
precedence including nested bold/italic, every LinkKind, transclusion
alt + attrs, resilience on unterminated links, and end-to-end
SyntaxRegistry dispatch.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/nuwiki-core/src/syntax/vimwiki/mod.rs

@@ -1,8 +1,40 @@
 //! Vimwiki syntax plugin.
-//!
-//! Phase 3 lands the lexer; the parser arrives in Phase 4 and the full
-//! `SyntaxPlugin` impl follows.
 
 pub mod lexer;
+pub mod parser;
 
 pub use lexer::{VimwikiLexer, VimwikiToken, VimwikiTokenKind};
+pub use parser::VimwikiParser;
+
+use crate::ast::DocumentNode;
+use crate::syntax::{Lexer, Parser, SyntaxPlugin};
+
+/// SyntaxPlugin facade: chains `VimwikiLexer` + `VimwikiParser` so the
+/// registry can hand out a single trait object per SPEC.md §6.3.
+#[derive(Debug, Default, Clone)]
+pub struct VimwikiSyntax;
+
+impl VimwikiSyntax {
+    pub fn new() -> Self {
+        Self
+    }
+}
+
+impl SyntaxPlugin for VimwikiSyntax {
+    fn id(&self) -> &str {
+        "vimwiki"
+    }
+
+    fn display_name(&self) -> &str {
+        "Vimwiki"
+    }
+
+    fn file_extensions(&self) -> &[&str] {
+        &[".wiki"]
+    }
+
+    fn parse(&self, text: &str) -> DocumentNode {
+        let tokens = VimwikiLexer::new().lex(text);
+        VimwikiParser::new().parse(tokens)
+    }
+}