Upgrade Zeus compatibility to 0.5.0.dev0

[brainx]

Summary

• vendor Zeus's exact 0.5.0.dev0 OpenAPI contract from commit f4a7af8a0ce802b3f9daeed0ee44958ef92abf1a
• add authenticated /ready client/CLI support, validate readiness schema version 6, and fail mutation preflights closed on not_ready
• replace the broad 0.3.N mutation gate with the exact reviewed 0.5.0.dev0 contract and pin the real-Zeus verifier to the same commit
• cover creation of kimi-k3-coding-bot using bot/template metadata only, with provider credentials and harness configuration remaining in Zeus
• update operator, staging, compatibility, threat-model, and changelog documentation

Cross-stack boundary

Zeus PR #20 remains the separate provider/template/audit change. This PR is only Olymp's compatibility side: it does not store Kimi credentials, select provider endpoints, or add direct harness integration.

Verification

• sh scripts/test.sh — 199 tests passed
• ruff format --check . — passed
• ruff check . — passed
• mypy olymp — passed with no issues in 19 source files
• sh -n scripts/*.sh — passed
• git diff --check — passed
• vendored OpenAPI SHA-256: 9ed13a758f3463308556f48fc133281db2953b069c4d8aaec5fae60c041359b1

Hosted CI

Run 30558321201 passed all 199 tests, 85% coverage, formatting, Ruff, and mypy before the repository Bandit gate reproduced two pre-existing findings in unchanged olymp/events.py: B608 at line 144 and B112 at line 176. The other matrix jobs were cancelled after that baseline failure.