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>

lua/nuwiki/config.lua

@@ -0,0 +1,6 @@
+-- lua/nuwiki/config.lua — user configuration schema and defaults.
+-- Implementation deferred to Phase 9 (Editor Glue).
+
+local M = {}
+
+return M

lua/nuwiki/init.lua

@@ -0,0 +1,6 @@
+-- lua/nuwiki/init.lua — Neovim entry point. Exposes setup() and install().
+-- Implementation deferred to Phase 9 (Editor Glue).
+
+local M = {}
+
+return M

lua/nuwiki/install.lua

@@ -0,0 +1,6 @@
+-- lua/nuwiki/install.lua — binary download / build-from-source.
+-- Implementation deferred to Phase 9 (Editor Glue).
+
+local M = {}
+
+return M

lua/nuwiki/lsp.lua

@@ -0,0 +1,6 @@
+-- lua/nuwiki/lsp.lua — vim.lsp.start wiring for the nuwiki-ls binary.
+-- Implementation deferred to Phase 9 (Editor Glue).
+
+local M = {}
+
+return M