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.

development/start-nvim.sh

@@ -2,25 +2,17 @@
 #
 # start-nvim.sh — launch Neovim with a minimal config that loads nuwiki.
 #
-# Builds the language server (release mode), symlinks it into `bin/` so
-# the plugin's default install path resolves, then spawns Neovim with
-# `--clean` and a generated `init.lua` that:
-#   * adds this repo to `runtimepath`
-#   * configures wiki_root to a scratch directory under
-#     $XDG_CACHE_HOME/nuwiki-dev/wiki
-#   * calls `require('nuwiki').setup({...})`
+# The plugin's install() downloads a pre-built release of nuwiki-ls for
+# your platform from the nuwiki-rs repository. On first launch a missing
+# binary is auto-downloaded via the bundled Vim script; set
+# NUWIKI_DEV_SKIP_BUILD=1 to skip the download entirely.
 #
 # Usage: ./development/start-nvim.sh [extra args...]
 #   ./development/start-nvim.sh                       # open the scratch wiki's index
 #   ./development/start-nvim.sh path/to/note.wiki     # open a specific file
 #   NUWIKI_DEV_WIKI=/tmp/foo ./development/start-nvim.sh
 #   NUWIKI_DEV_NO_SEED=1 ./development/start-nvim.sh      # use WIKI_DIR as-is (no scratch seeding)
-#   NUWIKI_DEV_SKIP_BUILD=1 ./development/start-nvim.sh   # reuse the cached binary
-#
-# The release binary is rebuilt on every launch so source changes
-# always reach the running LSP. `cargo build --release` is incremental,
-# so this is a fast no-op when nothing changed. Set
-# NUWIKI_DEV_SKIP_BUILD=1 to skip the build step entirely.
+#   NUWIKI_DEV_SKIP_BUILD=1 ./development/start-nvim.sh   # skip the download step
 #
 # Each launch starts clean: the scratch wiki is reseeded from a pristine
 # copy and the editor state (cache/data/config) is wiped, so stale edits