phase 19: editor glue v2

Server-side:
- New `folding.rs` module with `folding_ranges(ast, total_lines)`.
  Emits one fold per top-level heading (start → line before the
  next same-or-higher-level heading, or EOF) plus one per top-level
  list block. Nested headings fold inside their parent thanks to the
  level-aware end-line computation; sublists fold implicitly via
  their parent item's source span. `FoldingRangeKind::Region` is set
  on every fold so collapsing UIs render them as section folds.
- `Backend::folding_range` handler wires the module into
  `textDocument/foldingRange`; `ServerCapabilities.folding_range_provider`
  advertises it.
- `folding::line_count` exposed for the handler and tests; treats a
  trailing newline as a virtual empty line (the line LSP positions
  use for EOF).

Editor glue (Neovim primary, Vim minimal):
- `lua/nuwiki/commands.lua` — async `workspace/executeCommand`
  wrappers for every server command shipped through Phase 18. The
  open-* family handles `{ uri }` responses by opening the file
  (with `tab` / `split` variants). `check_links` and `find_orphans`
  hand results to `setqflist` + `:copen` for quickfix-style review.
  §13.1-deferred commands (`list.changeSymbol`, table rewriters,
  `link.pasteWikilink/pasteUrl`, `colorize`) stub out with
  `vim.notify` so users get a clear "not yet implemented" signal
  instead of an LSP "unknown command" error.
- `lua/nuwiki/keymaps.lua` — buffer-local default mappings. Subgroups
  (`list_editing`, `header_nav`, `diary`, `html_export`,
  `text_objects`) flip independently via the new
  `mappings.<group>` config. Heading promote/demote uses `g=`/`g-`
  to avoid clobbering Vim's built-in `=`/`-` operators.
- `lua/nuwiki/textobjects.lua` — `ah`/`ih` (around/inside heading)
  using a buffer scan for the heading-block boundary. The four
  remaining text objects from SPEC §12.10 wait until §13.1 lands
  the table/list rewriters they share infrastructure with.
- `lua/nuwiki/folding.lua` — pure regex `foldexpr` + `foldtext`
  fallback for clients without `foldingRange`. Same heading-block
  model as the server.
- `lua/nuwiki/ftplugin.lua` — single per-buffer attach entry point.
  `folding = 'lsp'` (default) uses Neovim 0.11+'s `vim.lsp.foldexpr`,
  falling back to the regex on older versions; `'expr'` forces the
  fallback; `'off'` skips folding setup.
- `lua/nuwiki/config.lua` — extends defaults with `mappings = {...}`
  (P10 keymap layer) and `folding` (P14 resolved).
- `ftplugin/nuwiki.vim` — declares every `:Vimwiki*` / `:Nuwiki*`
  command from SPEC §12.10 by inlining `lua require(...).fn()`
  bodies (no script-local function indirection so commands stay
  callable after re-source). Plain-Vim users get only the buffer
  options; they're expected to drive the LSP via vim-lsp / coc's
  built-in commands.

Health check (§12.10 additions):
- `:checkhealth nuwiki` now reports the count of `executeCommand`
  entries the server advertises, whether `foldingRange` capability
  was negotiated, and whether the configured HTML output directory
  exists + is writable. Default keymap subgroup status is also
  surfaced.

Tests: 8 new in `phase19_folding.rs` covering empty docs, single
heading → EOF, sibling headings each getting their own fold,
nested heading bounded by parent, top-level list folds, single-line
heading non-fold, fold-kind classification, and `line_count`
semantics. Total 377 tests pass; fmt + clippy clean.

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

SPEC.md

@@ -1382,14 +1382,12 @@ Deferred because the value proposition over the existing
 `workspace/rename` flow is marginal and the editor-side support is
 inconsistent across clients.
 
-### 13.3 v1.1 phase 19
+### 13.3 v1.1 status
 
-Tracked in §10 with status `⏳`. Not "missing" from earlier phases —
-it's future work in the v1.1 roadmap:
-
-- **Phase 19** — Editor glue v2: `:Vimwiki*` compat layer, default
-  keymaps, text objects, folding (P14 already resolved in favour of
-  LSP `foldingRange` + `foldexpr` fallback).
+All numbered phases through 19 are shipped. The remaining work is
+the §13.1 deferred Phase 14 command surface (table/list rewriters,
+link helpers, colorize) and the small follow-ups noted under §13.2 /
+§13.4.
 
 Earlier v1.1 phases now shipped:
 
@@ -1409,6 +1407,21 @@ Earlier v1.1 phases now shipped:
   picker commands: `nuwiki.wiki.listAll`, `nuwiki.wiki.select`,
   `nuwiki.wiki.openIndex`, `nuwiki.wiki.tabOpenIndex`, plus
   `nuwiki.wiki.gotoPage` for the `:VimwikiGoto` compat surface.
+- Phase 19 (editor glue v2) — LSP `textDocument/foldingRange`
+  provider (`folding::folding_ranges`) with heading-block + top-level
+  list semantics; advertised via `folding_range_provider`. A pure
+  Lua `foldexpr` fallback ships in `lua/nuwiki/folding.lua` for
+  clients without `foldingRange` support. `ftplugin/nuwiki.vim`
+  defines the full `:Vimwiki*` compat surface plus `:Nuwiki*`
+  aliases — every command that maps to a server-side `executeCommand`
+  is wired; §13.1-deferred commands stub out with a "not yet
+  implemented" notification so users get a clear signal. Default
+  buffer-local keymaps cover the working subset (checkbox toggle,
+  next task, heading promote/demote via `g=`/`g-`, diary navigation
+  via `<C-Up>`/`<C-Down>`, HTML export under `<Leader>wh*`). A
+  heading text object (`ah`/`ih`) ships now; `aH`/`iH`/`a\`/`i\`/
+  `ac`/`ic`/`al`/`il` land once the §13.1 table/list rewriters
+  arrive.
 
 ### 13.4 §9 syntax checklist status