feat(pause): emit events on pause and unpause

[1Judah]

Summary

Adds event emission to the contract's emergency pause and unpause entrypoints. This makes pause-state transitions observable off-chain so indexers, dashboards, and monitoring can react when the contract is halted or resumed.

Problem

The contract already exposed pause and unpause to halt and restore sensitive entrypoints, and is_paused to read the current state. However, transitioning the pause state produced no on-chain event. Clients could only detect a change by polling is_paused, and there was no canonical log entry recording when or in what order the contract was paused or unpaused.

Changes Made

• pause now publishes a paused event after setting the paused flag.
• unpause now publishes an unpaused event after clearing the paused flag.

Both entrypoints remain admin-gated via the existing require_admin helper, and both events are emitted only after the storage write succeeds. Only onchain/contracts/stellar_hunts/src/lib.rs was modified.

Implementation Details

The event follows the same pattern used elsewhere in the contract: env.events().publish with a Symbol topic. Because the pause flag carries no payload, the topic tuple is paired with an empty data value. Publishing after the state write keeps the event consistent with the persisted flag.

Closes #677

Closes #679

Closes #682

Closes #684

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[dzekojohn4]

LGTM