Fix /apps App Market page crash

Imported from GitHub pull request El-SaMa/oma#124 by @El-SaMa.

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Summary

• Production /apps threw: functions cannot be passed to Client Components (hrefForCategory).
• User-facing reference CCKECL (Next digest 3717799991).
• Replace the callback prop with a serializable hubPath string.

Test plan

• Open https://oma.lanetti.fi/apps after deploy (signed in)
• Category chips switch ?category= without crashing
• Public /app-market still works (default hubPath)