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/table_alignment.rs

@@ -0,0 +1,57 @@
+//! Cluster 7 — Markdown-style alignment markers on the header
+//! separator row (`|:--|--:|:--:|`) propagate to the AST and HTML.
+
+use nuwiki_core::ast::{BlockNode, TableAlign};
+use nuwiki_core::render::{HtmlRenderer, Renderer};
+use nuwiki_core::syntax::vimwiki::VimwikiSyntax;
+use nuwiki_core::syntax::SyntaxPlugin;
+
+fn parse(src: &str) -> nuwiki_core::ast::DocumentNode {
+    VimwikiSyntax::new().parse(src)
+}
+
+#[test]
+fn separator_row_with_no_anchors_yields_defaults() {
+    let doc = parse("| h1 | h2 |\n|----|----|\n| a  | b  |\n");
+    let table = match &doc.children[0] {
+        BlockNode::Table(t) => t,
+        _ => panic!("expected table"),
+    };
+    assert_eq!(
+        table.alignments,
+        vec![TableAlign::Default, TableAlign::Default]
+    );
+}
+
+#[test]
+fn left_right_center_anchors_parsed() {
+    let doc = parse("| a | b | c |\n|:---|---:|:---:|\n| 1 | 2 | 3 |\n");
+    let table = match &doc.children[0] {
+        BlockNode::Table(t) => t,
+        _ => panic!("expected table"),
+    };
+    assert_eq!(
+        table.alignments,
+        vec![TableAlign::Left, TableAlign::Right, TableAlign::Center]
+    );
+}
+
+#[test]
+fn html_renderer_emits_text_align_style() {
+    let doc = parse("| a | b | c |\n|:---|---:|:---:|\n| 1 | 2 | 3 |\n");
+    let out = HtmlRenderer::new().render_to_string(&doc).unwrap();
+    assert!(
+        out.contains(r#"<th style="text-align: left;"> a </th>"#),
+        "got: {out}"
+    );
+    assert!(out.contains(r#"<th style="text-align: right;"> b </th>"#));
+    assert!(out.contains(r#"<th style="text-align: center;"> c </th>"#));
+    assert!(out.contains(r#"<td style="text-align: left;"> 1 </td>"#));
+}
+
+#[test]
+fn render_without_alignment_omits_style_attr() {
+    let doc = parse("| a | b |\n|---|---|\n| 1 | 2 |\n");
+    let out = HtmlRenderer::new().render_to_string(&doc).unwrap();
+    assert!(!out.contains("text-align"));
+}