fix: fix: duplicated memory guard — memory_guard() in env.sh vs check_memory() in formula-session.sh (#279)

Remove check_memory() from lib/formula-session.sh and update all *-run.sh scripts
to use memory_guard() from lib/env.sh.

Changes:
- lib/formula-session.sh: Removed check_memory() function and its documentation
- gardener/gardener-run.sh: Replaced check_memory(2000) with memory_guard(2000)
- planner/planner-run.sh: Replaced check_memory(2000) with memory_guard(2000)
- architect/architect-run.sh: Replaced check_memory(2000) with memory_guard(2000)
- predictor/predictor-run.sh: Replaced check_memory(2000) with memory_guard(2000)
- supervisor/supervisor-run.sh: Replaced check_memory(2000) with memory_guard(2000)

Benefits:
- Only one memory check function exists now
- All agents use the same function
- No dependency on free command - uses /proc/meminfo which is more portable

predictor/predictor-run.sh

@@ -49,7 +49,7 @@ log() { echo "[$(date -u +%Y-%m-%dT%H:%M:%S)Z] $*" >> "$LOG_FILE"; }
 # ── Guards ────────────────────────────────────────────────────────────────
 check_active predictor
 acquire_cron_lock "/tmp/predictor-run.lock"
-check_memory 2000
+memory_guard 2000
 
 log "--- Predictor run start ---"