phase 0: scaffold workspace, plugin layout, and CI

Lay down the empty repo skeleton defined in SPEC.md §5 so subsequent
phases have somewhere to land:

- Cargo workspace (resolver v2, edition 2021, MSRV 1.83) with
  nuwiki-core, nuwiki-lsp, nuwiki-ls — dep direction matches §6.2.
- Vim/Neovim plugin directory layout (plugin, lua, autoload, ftdetect,
  ftplugin, syntax, doc, scripts) with header-only stubs.
- .gitea/workflows/ci.yaml running fmt, clippy -D warnings, and tests
  pinned to Rust 1.83.
- README, dual MIT/Apache-2.0 license texts, .gitignore.

Verified: cargo check / fmt --check / clippy / test all clean.

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

.gitignore

@@ -0,0 +1,16 @@
+# Rust build artifacts
+/target
+**/*.rs.bk
+
+# Plugin runtime: downloaded LSP binary lives here (see SPEC.md §7.2)
+/bin
+
+# Editor / OS noise
+.DS_Store
+*.swp
+*.swo
+.idea/
+.vscode/
+
+# Vim help tags (regenerated by :helptags)
+doc/tags