fix: agent-smoke.sh: use [(][)] instead of \(\) for BusyBox grep ERE compat

BusyBox grep (Alpine CI) does not treat \( as a literal paren in -E mode,
causing inject_formula to appear undefined even though it is defined in
lib/agent-session.sh. Using [(][)] is unambiguous in both GNU grep and
BusyBox grep.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.woodpecker/agent-smoke.sh

@@ -20,7 +20,7 @@ FAILED=0
 # Extract function names defined in a bash script (top-level or indented).
 get_fns() {
   local f="$1"
-  grep -Eo '[a-zA-Z_][a-zA-Z0-9_]+[[:space:]]*\(\)' "$f" 2>/dev/null \
+  grep -Eo '[a-zA-Z_][a-zA-Z0-9_]+[[:space:]]*[(][)]' "$f" 2>/dev/null \
     | sed 's/[[:space:]]*()//' | sort -u || true
 }