Mosh reliability hardening, TOFU host keys, and migration smoke tests

[ocnc]

Summary

• refine Mosh advanced settings and remove prediction plumbing
• add DEC charset handling and OSC 52 clipboard integration in terminal emulation
• replace accept-all SSH host key behavior with TOFU verification backed by a persisted trust store
• add host-key trust tests in SpecttyTransportTests
• introduce versioned SwiftData schemas (V1→V4) plus a migration plan that backfills nil Mosh fields
• add migration smoke tests in a new SpecttyTests target and shared scheme
• make app SwiftData container migration-aware and run in-memory during XCTest
• harden ConnectionStore save/fetch paths with explicit error logging

Commit Breakdown

• b7b22ce Refine mosh advanced settings and remove prediction plumbing
• 9a93ce6 Add DEC charset and OSC 52 clipboard handling
• df08331 Implement TOFU SSH host key verification
• af68891 Add staged SwiftData migration plan with smoke tests

Testing

• swift test (in Packages/SpecttyTransport)