[US-012] Quick-add live link from mobile share sheet

[leimo2011]

User Story

As a store owner on mobile,
I want to share a live link directly from Instagram/TikTok/etc to the Liemo app,
So that I can post my live link in seconds without opening the Liemo app first.

Acceptance Criteria

• Liemo app registers as share target on iOS and Android
• Shared URL auto-populates the link submission form
• One-tap publish after reviewing auto-filled details
• Works for Instagram, TikTok, Shopee, Facebook, YouTube

Estimate: 5 SP | Milestone: M2

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Epic: [EPIC-04] Live Link Aggregation Engine