fix: Array move ownership, selfhost -g flags, LSP workspace/symbol

Session 36: prevent UAF when Array is moved into a struct field (Nexus
headers), align selfhost cc flags with bootstrap debug/release, and add
workspace/symbol search to bux-lsp 0.6.

- Parser: zero headers after embedding so auto-drop is a no-op
- Request_WantsKeepAlive uses RequestHeader_Get again safely
- Selfhost: default -O0 -g; --release -O2 -DNDEBUG; BUX_CFLAGS
- LSP: workspace/symbol + smoke; version 0.6.0

tools/smoke_lsp_rename.sh

@@ -59,8 +59,8 @@ if ! grep -q 'renameProvider' "$TMP/out.txt"; then
   echo "FAIL: initialize missing renameProvider"
   exit 1
 fi
-if ! grep -q '0.5.0' "$TMP/out.txt"; then
-  echo "WARN: version not 0.5.0 in initialize (may be ok)"
+if ! grep -qE '0\.[56]\.0' "$TMP/out.txt"; then
+  echo "WARN: unexpected bux-lsp version in initialize"
 fi
 
 # Rename workspace edit should propose "total"