chore(dev): always rebuild release binary in start scripts

ensure_binary used to short-circuit whenever bin/nuwiki-ls existed,
which left vim/nvim running an outdated LSP after every source change.
Now always invoke cargo build (incremental, so a no-op when nothing
changed) and refresh the symlink + log the build timestamp. Add
NUWIKI_DEV_SKIP_BUILD=1 for the rare opt-out.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

start-nvim.sh

@@ -14,6 +14,12 @@
 #   ./start-nvim.sh                       # open the scratch wiki's index
 #   ./start-nvim.sh path/to/note.wiki     # open a specific file
 #   NUWIKI_DEV_WIKI=/tmp/foo ./start-nvim.sh
+#   NUWIKI_DEV_SKIP_BUILD=1 ./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.
 #
 # Tested with Neovim 0.10+. State (cache/data/config) lives under
 # $XDG_CACHE_HOME/nuwiki-dev/ so your real Neovim install stays
@@ -34,14 +40,19 @@ log() { printf '\033[1;34m[nuwiki-dev]\033[0m %s\n' "$*"; }
 ensure_binary() {
   local bin="$REPO_ROOT/bin/nuwiki-ls"
   local built="$REPO_ROOT/target/release/nuwiki-ls"
-  if [[ -x "$bin" ]]; then
-    return
+  if [[ "${NUWIKI_DEV_SKIP_BUILD:-0}" == "1" ]]; then
+    if [[ ! -x "$bin" ]]; then
+      log "NUWIKI_DEV_SKIP_BUILD=1 but $bin is missing — building anyway"
+    else
+      log "NUWIKI_DEV_SKIP_BUILD=1 — using existing $bin"
+      return
+    fi
   fi
   log "building nuwiki-ls (release)…"
   cargo build --release -p nuwiki-ls --manifest-path "$REPO_ROOT/Cargo.toml"
   mkdir -p "$REPO_ROOT/bin"
   ln -sf "$built" "$bin"
-  log "binary ready: $bin"
+  log "binary ready: $bin (built $(date -r "$built" '+%Y-%m-%d %H:%M:%S'))"
 }
 
 seed_wiki() {