Emit rich lifecycle events for every state change in Crowdfunding

[nanaf6203-bit]

Problem Statement

Crowdfunding misses events on partial cancellations, refund queue updates, milestone transitions.

Why it matters

Off-chain indexers rely on event completeness to power investor UIs.

Technical Context

Add events for: CampaignPaused, CampaignResumed, MilestoneApproved/Rejected, RefundBatchStarted, RefundBatchCompleted.

Expected Outcome

Every state transition has a corresponding event with topic fields.

Acceptance Criteria

1. New events appear in cargo contract events.
2. SDK updated.
3. New regression coverage in tests/crowdfunding_events.rs.
4. Doc updated.

Implementation Notes

Hand-add events; add doc.

Files or modules likely to be affected

contracts/crowdfunding/src/lib.rs.

Dependencies

None.

Difficulty level

MEDIUM.

Estimated effort

S (~1 day).

[DevRushd]

@DevRushd has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

I would love to fix this issue. Can you please assign it to me

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[intelliDean]

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Hi. I'd like to work on this issue

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[SugaretaNajja]

@SugaretaNajja has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

can i tackle this issue?

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