refactor(tests): group test files by feature, drop phase/cluster naming

Restructures the integration test layout so each file is named after
what it covers, not the implementation phase it landed in.

nuwiki-core (renames only):
  vimwiki_lexer            → lexer
  vimwiki_parser           → parser
  vimwiki_tags             → tags
  vimwiki_table_alignment  → table_alignment
  diary_period             → diary
  list_continuation        → lists
  transclusion_attrs       → transclusion
  + table colspan/rowspan tests moved here from parity_cluster_1

nuwiki-lsp (renames + merges + one split):
  cluster_a_list_rewriters       → commands_lists
  cluster_b_table_rewriters      → commands_tables
  cluster_c_link_helpers +
    phase19_followlink_creates   → commands_links
  phase13_rename_commands        → commands_files
  phase17_colorize               → commands_colorize
  phase17_html_export            → html_export
  phase15_link_health            → link_health
  phase18_multi_wiki             → multi_wiki
  phase19_folding                → folding
  nav                            → navigation
  lsp_helpers                    → helpers
  phase16_diary +
    diary_frequency              → diary
  phase11_plumbing +
    parity_cluster_1 (config)    → index_and_config
  tags_index_and_lsp +
    phase17_backfill             → commands_tags
  phase14_edit_commands          → split into
    commands_checkboxes,
    commands_headings,
    commands_tasks

Net: 30 → 28 integration-test files. 456 → 455 tests (the one
removed test was a dummy `paragraph_render_is_unchanged` whose only
purpose was to keep a `ParagraphNode` import alive in
parity_cluster_1; the import is exercised elsewhere now).

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

crates/nuwiki-core/tests/html_renderer.rs

@@ -2,7 +2,10 @@
 //!
 //! Pipeline: source text → `VimwikiSyntax::parse` → `HtmlRenderer::render`.
 
-use nuwiki_core::ast::LinkTarget;
+use nuwiki_core::ast::{
+    BlockNode, DocumentNode, InlineNode, LinkTarget, Span, TableCellNode, TableNode, TableRowNode,
+    TextNode,
+};
 use nuwiki_core::render::{HtmlRenderer, Renderer};
 use nuwiki_core::syntax::vimwiki::VimwikiSyntax;
 use nuwiki_core::syntax::SyntaxPlugin;
@@ -12,6 +15,42 @@ fn render(src: &str) -> String {
     HtmlRenderer::new().render_to_string(&doc).unwrap()
 }
 
+fn span_cell(text: &str, col_span: bool, row_span: bool) -> TableCellNode {
+    let s = Span::default();
+    TableCellNode {
+        span: s,
+        children: vec![InlineNode::Text(TextNode {
+            span: s,
+            content: text.into(),
+        })],
+        col_span,
+        row_span,
+    }
+}
+
+fn span_table(rows: Vec<Vec<TableCellNode>>, has_header: bool) -> DocumentNode {
+    let span = Span::default();
+    let rows: Vec<TableRowNode> = rows
+        .into_iter()
+        .enumerate()
+        .map(|(i, cells)| TableRowNode {
+            span,
+            cells,
+            is_header: has_header && i == 0,
+        })
+        .collect();
+    DocumentNode {
+        span,
+        metadata: Default::default(),
+        children: vec![BlockNode::Table(TableNode {
+            span,
+            rows,
+            has_header,
+            alignments: Vec::new(),
+        })],
+    }
+}
+
 // ===== Block elements =====
 
 #[test]
@@ -290,3 +329,56 @@ fn x() {}
         );
     }
 }
+
+// ===== Table colspan / rowspan =====
+
+#[test]
+fn colspan_marker_folds_into_lead_cell() {
+    // | a | b | c |
+    // | d | > | e |    → second row has b spanning 2 cols (cell index 1 is >)
+    let doc = span_table(
+        vec![
+            vec![
+                span_cell("a", false, false),
+                span_cell("b", false, false),
+                span_cell("c", false, false),
+            ],
+            vec![
+                span_cell("d", false, false),
+                span_cell(">", true, false),
+                span_cell("e", false, false),
+            ],
+        ],
+        false,
+    );
+    let out = HtmlRenderer::new().render_to_string(&doc).unwrap();
+    assert!(out.contains(r#"<td colspan="2">d</td>"#), "got: {out}");
+    assert!(!out.contains(r#"class="col-span""#));
+}
+
+#[test]
+fn rowspan_marker_folds_into_lead_cell_above() {
+    let doc = span_table(
+        vec![
+            vec![span_cell("a", false, false), span_cell("b", false, false)],
+            vec![span_cell("c", false, false), span_cell("\\/", false, true)],
+        ],
+        false,
+    );
+    let out = HtmlRenderer::new().render_to_string(&doc).unwrap();
+    assert!(out.contains(r#"<td rowspan="2">b</td>"#), "got: {out}");
+}
+
+#[test]
+fn no_spans_emits_no_table_attrs() {
+    let doc = span_table(
+        vec![
+            vec![span_cell("a", false, false), span_cell("b", false, false)],
+            vec![span_cell("c", false, false), span_cell("d", false, false)],
+        ],
+        false,
+    );
+    let out = HtmlRenderer::new().render_to_string(&doc).unwrap();
+    assert!(!out.contains("colspan="));
+    assert!(!out.contains("rowspan="));
+}