install-x64.sh: unguarded openclaw config set calls can abort steps on ConfigMutationConflictError

[KrasimirKralev]

Same bug class as #192 fixed for the Jetson installer, but in the x64 path:

• install-x64.sh:282 — as_user "$OPENCLAW_BIN" config set gateway.controlUi.allowInsecureAuth true --json runs under set -euo pipefail with no retry and no || true. A ConfigMutationConflictError (OpenClaw 2026.6.x optimistic concurrency — triggered by the live gateway or the CLI's own state migrations) aborts the step mid-update.
• Lines ~354/369/371/372 take the opposite shortcut (2>/dev/null || true) — conflicts there are silently swallowed and the config is simply not applied.

Note x64 has no gateway-pre-start.sh, so the auth/controlUi writes can't be deferred the way #192 did for Jetson — they need the retry treatment (port oc_config_set from install.sh), and the silently-swallowed ones should at least log.

Found during the #192 review.

[KrasimirKralev]

Triage: bug, same class as the already-fixed #192 (Jetson installer) but in the x64 path — unguarded openclaw config set under set -euo pipefail aborts on ConfigMutationConflictError. Well-scoped: guard the ~5 call sites with the same retry helper #192 introduced.