feat: add Ultra provider tier and portable capability assignments

[atomantic]

Summary

Provider tiers already drive CoS selection, thinking-level routing, prompt stages, and agent dispatch guidance. Add an explicit Ultra capability tier for exceptional reasoning, with Astra and Fable defaults for the corresponding shipped CLI providers. Unconfigured Ultra requests fall back to Heavy and then the provider default.

Provider settings can save the fourth mapping, Prompt Manager can select Ultra, and CoS task/role model assignments can request capability tiers instead of exact model IDs. Dispatch guidance and learning displays use provider-neutral tier language. Existing heuristics, schedules, exact model pins, and reasoning-effort choices retain their behavior; the migration fills missing Ultra fields and offers Fable additively on standard Claude catalogs without changing existing pins. See docs/MODEL_TIERS.md for the usage audit and assignment guidance.

Test plan

• Focused server suites for tier selection, provider fallback, staged execution, provider persistence/seed parity, migration compatibility, dispatch labels, orchestration guidance, capability inventory, and local-model healing.
• Provider form persistence and Prompt Manager tests.
• Client production build and changed-client-file lint.
• Optional Claude review ran in an enforced restricted/read-only profile; substantive findings were fixed and verified within the configured one-round cap. Its prose-prefixed output was formally inconclusive under the strict verdict format.