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-vim.sh

@@ -7,18 +7,18 @@
 # the dev cache on first run so the LSP integration is exercisable
 # without polluting your real Vim install.
 #
+# 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-vim.sh [extra args...]
 #   ./development/start-vim.sh                        # open the scratch wiki's index
 #   ./development/start-vim.sh path/to/note.wiki      # open a specific file
 #   NUWIKI_DEV_WIKI=/tmp/foo ./development/start-vim.sh
 #   NUWIKI_DEV_NO_LSP=1 ./development/start-vim.sh        # skip vim-lsp setup
 #   NUWIKI_DEV_NO_SEED=1 ./development/start-vim.sh       # use WIKI_DIR as-is (no scratch seeding)
-#   NUWIKI_DEV_SKIP_BUILD=1 ./development/start-vim.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-vim.sh    # skip the download step
 #
 # Each launch starts clean: the scratch wiki is reseeded from a pristine
 # copy and the editor state (viminfo/swap/undo) is wiped, so stale edits