Pausable contract: global emergency pause flag

[greatest0fallt1me]

Description

Global pause controlled by admin address blocking mutating ops except unpause (define scope).

Requirements and context

• Document centralization tradeoff.
• Events on pause/unpause.

Suggested execution

• Fork the repository and create a branch (example below).
• Implement the changes in the StreamPay-Contracts Soroban crate (streampay-contracts).
• Keep the contract secure, tested, and documented; prefer small, reviewable diffs.

git checkout -b feature/global-emergency-pause

Implementation targets

• lib.rs.
• Tests: paused vs unpaused paths.

Tests and validation

• Add or extend contract tests for this scope.

• Cover edge cases; paste summarized test output and security notes in the PR.

• Run cargo test in StreamPay-Contracts.

• Cover edge cases; capture test output and short security notes in the PR description.

Guidelines

• Target minimum 95% test coverage for touched contract code (or justify gaps explicitly).
• Clear documentation (rustdoc / project docs as specified).
• Timeframe: 96 hours from assignment.

Example commit message

feat(contracts): global emergency pause for mutators