Fix: plugin not loading at startup (missing activation.onStartup) — bump 1.2.4

[pallaoro]

Problem

ClawFlow's openclaw.plugin.json has no activation field. Per current OpenClaw
plugin manifest semantics (docs/plugins/manifest.md):

Omitting onStartup no longer implicitly startup-loads the plugin; explicit
activation metadata is required for startup or other specific triggers.

So the gateway discovers clawflow (status: loaded) but never runs its
register(). Observable on a live gateway via openclaw plugins list --json:

id=clawflow status=loaded toolNames=[] httpRoutes=0

Consequences: the flow_* tools are never registered, the approval hook never
wires up, and — when config.serve is set — the flow HTTP server never starts.
That silently breaks every inbound flow entry point (HTTP triggers,
webhook-to-flow dispatch): the flows tunnel origin has nothing listening, so calls
return 502.

Fix

Add explicit activation: { onStartup: true } to the manifest. ClawFlow registers
tools, a hook, and a long-lived server — all of which must run at gateway startup.

"activation": { "onStartup": true }

Also aligns the manifest version (was stale at 1.2.2) with the package version,
and bumps both to 1.2.4.

Verification

On a live gateway, with the manifest patched and config.serve.port set:

[plugins] [clawflow] flow server listening on :<port>/flows/:flowName/run
GET /flows/health -> {"ok":true,"flowsDir":"..."} [200]

Before the patch (no activation), the same gateway never bound the port and logged
no clawflow server line.