feat(render): list_ignore_newline / text_ignore_newline = false → <br>

Implements the deferred half of these options: a soft line break inside a
paragraph / list item can render as <br /> instead of a space.

- Parser: soft breaks now emit a dedicated InlineNode::SoftBreak node
  (parse_inline_seq K::Newline + the list-continuation synthetic join) instead
  of collapsing to Text(" "). Added SoftBreakNode + the variant.
- All inline consumers treat SoftBreak as whitespace: AST visitor (no-op),
  text extraction (index.rs + lib.rs → space), nav/semantic_tokens span_of_inline,
  semantic emit (skip like Text), parser span_of_inline.
- Renderer: render_inlines_break renders top-level SoftBreaks as the
  context-specific string; render_paragraph uses text_ignore_newline,
  render_list_item uses list_ignore_newline; default render_inline → space.
  with_newline_handling builder; export.rs wires both from HtmlConfig.

Default (true/true = upstream default) behaviour is unchanged (space). Updated
3 core tests + 1 parser test that asserted the old Text(" ") shape to treat
SoftBreak as whitespace. New test render_page_html_ignore_newline_controls_soft_breaks.

Gap doc: P3 Config item closed — only the deferred markdown cluster remains.
Full rust suite + clippy clean; Neovim 307, Vim 301/18/21.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

@@ -39,7 +39,7 @@ use crate::ast::{
     InlineNode, ItalicNode, KeywordNode, LinkKind, LinkTarget, ListItemNode, ListNode, ListSymbol,
     MathBlockNode, MathInlineNode, PageMetadata, ParagraphNode, PreformattedNode, RawUrlNode, Span,
     StrikethroughNode, SubscriptNode, SuperscriptNode, TableCellNode, TableNode, TableRowNode,
-    TagNode, TagScope, TextNode, TransclusionNode, WikiLinkNode,
+    SoftBreakNode, TagNode, TagScope, TextNode, TransclusionNode, WikiLinkNode,
 };
 use crate::syntax::{Parser, TokenStream};
 
@@ -596,14 +596,11 @@ impl<'a> ParseState<'a> {
                     }
                 }
             }
-            // Insert a synthetic " " between the previous content and
-            // the continuation so the rendered text flows naturally.
+            // Insert a soft break between the previous content and the
+            // continuation so the rendered text flows naturally (and honours
+            // `*_ignore_newline`).
             if !children.is_empty() {
-                let span = first.span;
-                children.push(InlineNode::Text(TextNode {
-                    span,
-                    content: " ".into(),
-                }));
+                children.push(InlineNode::SoftBreak(SoftBreakNode { span: first.span }));
             }
             let cont = parse_inline_seq(&buf);
             children.extend(cont);
@@ -1008,11 +1005,10 @@ fn parse_inline_seq(toks: &[VimwikiToken]) -> Vec<InlineNode> {
                 i += 1;
             }
             K::Newline => {
-                // Soft break inside a multi-line block: render as space.
-                out.push(InlineNode::Text(TextNode {
-                    span: token.span,
-                    content: " ".into(),
-                }));
+                // Soft break inside a multi-line block. A dedicated node lets
+                // the renderer honour `*_ignore_newline` (space vs `<br />`);
+                // other consumers treat it as whitespace.
+                out.push(InlineNode::SoftBreak(SoftBreakNode { span: token.span }));
                 i += 1;
             }
             K::BoldDelim => {
@@ -1454,5 +1450,6 @@ fn span_of_inline(node: &InlineNode) -> Span {
         InlineNode::ExternalLink(n) => n.span,
         InlineNode::Transclusion(n) => n.span,
         InlineNode::RawUrl(n) => n.span,
+        InlineNode::SoftBreak(n) => n.span,
     }
 }