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/tests/test-keymaps.sh

@@ -5,7 +5,7 @@
 #
 # The Lua harness needs a real LSP attachment (most keymaps dispatch
 # `workspace/executeCommand`), so we:
-#   1. ensure `bin/nuwiki-ls` is built (release),
+#   1. download `bin/nuwiki-ls` from the nuwiki-rs releases,
 #   2. spin up a scratch wiki under a temp dir,
 #   3. invoke `nvim --headless` with a minimal init that loads the
 #      plugin + calls `setup()`, then sources the harness Lua.
@@ -20,15 +20,34 @@ trap 'rm -rf "$TMP"' EXIT
 
 log() { printf '\033[1;34m[keymap-test]\033[0m %s\n' "$*"; }
 
-# Always rebuild the LSP binary so harness runs against current sources.
-# A previous version only built when the symlink was missing, which let
-# stale binaries pass tests against unrelated code — incremental cargo
-# build is fast, so just always run it.
+# Download the LSP binary from nuwiki-rs releases (falls back to cargo build).
 BIN="$REPO_ROOT/bin/nuwiki-ls"
-log 'building nuwiki-ls (release, incremental)…'
-cargo build --release -p nuwiki-ls --manifest-path "$REPO_ROOT/Cargo.toml" >/dev/null
-mkdir -p "$REPO_ROOT/bin"
-ln -sf "$REPO_ROOT/target/release/nuwiki-ls" "$BIN"
+log 'downloading nuwiki-ls…'
+if [[ ! -x "$BIN" ]]; then
+  vim -e -s -c "source $REPO_ROOT/scripts/download_bin.vim" -c "q" >/dev/null 2>&1 || true
+fi
+
+# If download failed, fall back to cargo build from nuwiki-rs.
+if [[ ! -x "$BIN" ]]; then
+  log "download failed, falling back to cargo build from nuwiki-rs…"
+  rs_repo="$REPO_ROOT/nuwiki-rs"
+  if [[ ! -f "$rs_repo/Cargo.toml" ]]; then
+    log "cloning nuwiki-rs …"
+    git clone --depth 1 https://code.gfran.co/gffranco/nuwiki-rs.git "$rs_repo"
+  fi
+  cargo build --release -p nuwiki-ls --manifest-path "$rs_repo/Cargo.toml" >/dev/null
+  if [[ ! -f "$rs_repo/target/release/nuwiki-ls" ]]; then
+    echo 'FAIL: could not build nuwiki-ls binary' >&2
+    exit 1
+  fi
+  mkdir -p "$REPO_ROOT/bin"
+  ln -sf "$rs_repo/target/release/nuwiki-ls" "$BIN"
+fi
+
+if [[ ! -x "$BIN" ]]; then
+  echo 'FAIL: could not obtain nuwiki-ls binary' >&2
+  exit 1
+fi
 
 mkdir -p "$TMP/wiki"
 echo "= seed =" > "$TMP/wiki/index.wiki"