fix(manifest): declare memory kind and register memory capability

[YOMXXX]

Summary

Fixes #119 — openclaw doctor reports "memory slot plugin not found" even though memory-tencentdb is loaded and serving four-layer memory.

Root cause

The host's slot loader matches memory plugins via hasKind(record.kind, "memory") and only accepts registerMemoryCapability(...) from plugins whose manifest declares that kind. memory-tencentdb's manifest never set kind, and the plugin never called registerMemoryCapability. So from the host's view the memory slot is empty — doctor surfaces that as the missing-slot warning.

Change

• openclaw.plugin.json: add "kind": "memory" so the loader recognizes this plugin as a memory-kind candidate.
• index.ts: in register(), feature-detect api.registerMemoryCapability and call it with an empty capability {} to claim the slot. The slot loader requires kind: "memory" before accepting the call (verified against the bundled OpenClaw SDK).
  • Wrapped in try/catch and feature-detected via typeof === "function" so older OpenClaw hosts (before the API existed) still load the plugin without error.
  • Logged at debug (success) / warn (failure) — non-fatal either way.

Empty {} is sufficient for slot-occupancy. promptBuilder / runtime / publicArtifacts can be wired later if we want the host to drive prompt sections or flush plans through its own memory pipeline; that's a follow-up, not part of this fix.

Test plan

• Build still passes (npm run build)
• On a fresh OpenClaw install, openclaw doctor no longer reports "memory slot plugin not found"
• On an OpenClaw host older than the registerMemoryCapability API, the plugin still loads and runtime hooks fire (feature detection skips the call)

[Maxwell-Code07]

Thanks for the contribution! We've received your PR fixing the OpenClaw doctor false alarm and will review it internally. We'll get back to you once we have results. Appreciate you tracking down this manifest issue!