feat: add canonical execution outcomes

[Joncallim]

Summary

• add a versioned, idempotent execution_outcomes ledger and migration
• normalize admission blocks and terminal work-package results into bounded, redacted outcomes
• document the contract in ADR 0010 and add focused regression coverage

Why

Forge previously mixed transport state, semantic results, and free-text errors, making execution evidence unsafe to compare. This introduces the shared outcome boundary required by #185.

Validation

• cd web && npm test -- --run __tests__/execution-outcomes.test.ts __tests__/work-package-handoff-db.test.ts
• git diff --check

Known baseline limits

• npx tsc --noEmit remains blocked by pre-existing malformed or missing implicit type packages.
• Drizzle snapshots stop at migration 0026 while the journal already reaches 0028, so generating a new snapshot triggers unrelated interactive prompts. Migration 0029 and the journal entry follow the repositorys existing migration convention.