fix: unpause() clears AutoPaused to prevent stuck contract (#452)

[Nife-tanny]

Description

Fixes the contract getting stuck in an auto-paused state when the campaign that triggered the automatic pause is subsequently cancelled.

Root Cause

When a burst contribution triggers an automatic pause, resume_campaign calls require_active_campaign before clearing the AutoPaused flag. If the triggering campaign is cancelled (making it inactive), resume_campaign fails at the require_active_campaign check, leaving AutoPaused permanently true with no way to clear it — the contract is stuck.

Fix

Updated unpause() in src/admin.rs to clear both pause flags:

env.storage().instance().set(&AdminKey::Paused, &false);
env.storage().instance().set(&AdminKey::AutoPaused, &false);

Previously unpause() only cleared Paused, leaving AutoPaused untouched with no public recovery path.

Changes

• src/admin.rs: Added env.storage().instance().set(&AdminKey::AutoPaused, &false); to unpause()
• CHANGELOG.md: Added entry for the fix under [Unreleased] → ### Fixed
• Authorization unchanged — assert_admin still gates the function
• Storage pattern matches existing conventions (instance storage, TTL bump before writes)
• Event emission unchanged

Tests

The existing regression test test_unpause_clears_auto_pause_when_resume_campaign_blocked in src/tests/test_campaigns.rs validates:

1. AutoPaused = true → operations blocked
2. unpause() called → both flags cleared
3. Operations resume successfully
4. resume_campaign still fails for cancelled campaigns (unchanged behavior)
5. Contract fully operational after unpause()

Closes #452