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>

Cargo.toml

@@ -0,0 +1,22 @@
+[workspace]
+resolver = "2"
+members = [
+    "crates/nuwiki-core",
+    "crates/nuwiki-lsp",
+    "crates/nuwiki-ls",
+]
+
+[workspace.package]
+version = "0.1.0"
+edition = "2021"
+rust-version = "1.83"
+authors = ["Gabriel Fróes Franco <gffranco@gmail.com>"]
+license = "MIT OR Apache-2.0"
+repository = "https://code.gfran.co/gffranco/nuwiki"
+homepage = "https://code.gfran.co/gffranco/nuwiki"
+
+[workspace.lints.rust]
+unsafe_code = "forbid"
+
+[workspace.lints.clippy]
+all = { level = "warn", priority = -1 }