feat(stellar): circuit-breaker pause for stealth-sender and wraith-names

[Meet-hybrid]

Description
Currently, only stealth‑announcer supports a pause guard. If a live vulnerability is disclosed against stealth‑sender or wraith‑names, the only mitigation is a full upgrade—an hours‑long, multi‑sig process. This PR introduces a lightweight circuit‑breaker mechanism to allow immediate pausing of contract activity while keeping withdrawals available so users can always exit safely.

Implementation
Added Paused storage and pause(), unpause(), and is_paused() functions gated by Admin.

Wrapped all state‑mutating entrypoints (except withdraw, reveal, and lookup) with require_not_paused().

Emitted Paused and Unpaused events following the same topic pattern used in stealth‑announcer.

Updated PAUSE.md and MULTISIG.md to document the new guarded surfaces.

Referenced stealth‑announcer/src/pause.rs for consistency in event design.

Acceptance Criteria
cargo test --workspace covers pause/unpause and paused‑call rejection for both contracts.

withdraw on stealth‑sender and reveal/lookup on wraith‑names remain callable while paused (verified by dedicated tests).

SAC Smoke and Futurenet integration tests remain green.

PAUSE.md lists all guarded entrypoints per contract.

Files Touched
stealth‑announcer/src/pause.rs (reference)
stealth‑sender/src/lib.rs
wraith‑names/src/lib.rs
PAUSE.md
EVENT_TOPIC_DESIGN.md

closes #100

[drips-wave]

@Meet-hybrid Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits

[truthixify]

Merge conflicts against develop after the merge cascade. Rebase and the stellar step should behave differently against current develop.