Accept opaque Zalo chat IDs for outbound sends

OpenClaw's Zalo channel used a shared numeric target predicate, so valid Zalo Bot Platform chat_id strings such as reported hex-like IDs and documented dotted examples failed local target resolution before delivery.

Replaced the Zalo-local target predicate with an opaque nonblank chat ID check, kept blank and prefix-only targets rejected, left shared target heuristics unchanged, and added resolver coverage for numeric, hex-like, dotted, prefixed, ordinary, and blank targets.

• Unblocks scheduled and scripted proactive Zalo notifications for valid nonnumeric chat_id values.
• Keeps the behavior scoped to the Zalo plugin instead of weakening shared outbound target rules.
• Preserves contribution credit from the superseded contributor PR through the landed co-authored commit.

• Maintainer comment on #93689 confirms the same final two-file fix landed in #101548 with Co-authored-by credit preserved.
• Landed commit message includes Co-authored-by: Goutam Adwant <workwithgoutam@gmail.com>.
• Maintainer validation included 34 focused tests and a real dry-run openclaw message send path for abc.xyz.