Remove Rust code, delegate server to nuwiki-rs repo

Delete all Rust crates (crates/) and Cargo files. The nuwiki-ls binary
is now built in the separate nuwiki-rs repository and downloaded at
install time from the Gitea release assets, with a cargo build fallback
that clones nuwiki-rs.

Update all documentation to reflect the split repo layout.

README.md

@@ -6,7 +6,8 @@ nuwiki replaces the original [vimwiki](https://github.com/vimwiki/vimwiki)
 plugin while keeping its file format, keymaps, and `:Vimwiki*` command
 surface intact. The substantive work happens in a Rust LSP daemon — Vim
 and Neovim are thin client layers that wire up keystrokes and display
-results.
+results. The `nuwiki-ls` binary is distributed separately in the
+[nuwiki-rs](https://code.gfran.co/gffranco/nuwiki-rs) repository.
 
 ## Features
 
@@ -72,9 +73,12 @@ results.
 
 The plugin ships a `nuwiki-ls` binary that the editor talks to over LSP
 stdio. The `install()` helper downloads a pre-built release for your
-platform, falling back to `cargo build --release` if no asset matches.
-You can run it any time with `:NuwikiInstall` (works in both Vim and
-Neovim) instead of relying on a plugin-manager build hook.
+platform from the [nuwiki-rs](https://code.gfran.co/gffranco/nuwiki-rs)
+repository. If the download fails (or `curl`/`tar` are unavailable), it
+falls back to cloning nuwiki-rs and building with `cargo` — which requires
+a Rust toolchain (1.83+ stable). You can run install manually any time with
+`:NuwikiInstall` (works in both Vim and Neovim) instead of relying on a
+plugin-manager build hook.
 
 ### Requirements
 
@@ -86,8 +90,10 @@ Neovim) instead of relying on a plugin-manager build hook.
   [`coc.nvim`](https://github.com/neoclide/coc.nvim) — both
   auto-registered, no manual config (see [Vim LSP client
   setup](#vim-lsp-client-setup)).
-- **Rust toolchain (1.83+ stable)** — only needed when building the
-  binary from source; pre-built release downloads skip this.
+- **curl + tar** — for downloading pre-built release binaries.
+- **Rust toolchain (1.83+ stable)** — only needed when building
+  the binary from source as a fallback (when no pre-built asset matches
+  your platform or curl/tar are unavailable).
 
 ### lazy.nvim
 
@@ -126,10 +132,13 @@ call dein#add('gffranco/nuwiki', {
 
 ```sh
 git clone https://code.gfran.co/gffranco/nuwiki ~/.vim/pack/gffranco/start/nuwiki
-cd ~/.vim/pack/gffranco/start/nuwiki && cargo build --release -p nuwiki-ls
-mkdir -p bin && cp target/release/nuwiki-ls bin/
+cd ~/.vim/pack/gffranco/start/nuwiki && vim -e -s -c "source scripts/download_bin.vim" -c "q"
 ```
 
+If the download fails, `download_bin.vim` will clone
+[nuwiki-rs](https://code.gfran.co/gffranco/nuwiki-rs) and build from source
+(requires `cargo`).
+
 ### Vim LSP client setup
 
 Neovim 0.11+ registers the server through its built-in LSP client
@@ -196,9 +205,13 @@ aliases.
 ./development/start-vim.sh    # same, for plain Vim (clones vim-lsp on first run)
 ```
 
-Both scripts build the LSP binary, seed a scratch wiki, and launch the
+Both scripts download the LSP binary, seed a scratch wiki, and launch the
 editor against an isolated state dir under `$XDG_CACHE_HOME/nuwiki-dev`.
 
+Alternatively, set `g:nuwiki_binary_path` to point at a `nuwiki-ls`
+binary built from the [nuwiki-rs](https://code.gfran.co/gffranco/nuwiki-rs)
+repository.
+
 ---
 
 ## Configuration
@@ -441,7 +454,6 @@ For users configuring without Lua.
 | `g:nuwiki_no_folding` | `0` | `1` skips foldexpr setup |
 | `g:nuwiki_mouse_mappings` | `0` | `1` enables mouse maps |
 | `g:nuwiki_binary_path` | _(auto)_ | path to a prebuilt `nuwiki-ls` binary, bypassing the bundled one |
-| `g:nuwiki_build_from_source` | `0` | `1` builds the binary with `cargo` instead of downloading a release |
 | `g:nuwiki_no_calendar` | `0` | `1` opts out of calendar-vim integration |
 | `g:nuwiki_auto_chdir` | `0` | `1` `:lcd` into the wiki root when a wiki buffer becomes current |
 | `g:nuwiki_auto_header` | `0` | `1` insert a level-1 header from the filename on new wiki pages |