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

docs/BuildAndTest.md

@@ -146,12 +146,14 @@ make bench-nexus     # wrk throughput vs apps/nexus /api/health
 ### Debug builds (E.4)
 
 ```bash
-./buxc build              # -O0 -g, #line → .bux (gdb-friendly)
-./buxc build --release    # -O2, no debug maps
+./buxc build              # -O0 -g, #line → .bux (gdb-friendly; bootstrap)
+./buxc build --release    # -O2 -DNDEBUG, no #line / -g
+# Selfhost (buxc2) same --release / default -O0 -g; #line maps bootstrap-only for now
+export BUX_CFLAGS="-fno-omit-frame-pointer"   # optional extra cc flags
 gdb --args ./build/myapp
 #   (gdb) break Main
 #   (gdb) run
-#   (gdb) list            # shows Bux source via #line
+#   (gdb) list            # shows Bux source via #line (bootstrap)
 ```