Manifesto/site overclaim: proxy budget and rate-limit enforcement

[mostlydev]

Part of #302 (Phase 0).

Problem

The manifesto claims enforcement that does not exist:

• MANIFESTO.md Core Principle 6: "the proxy enforces budgets and rate limits" — nothing enforces budgets or rate limits today.
• MANIFESTO.md §VII: "it enforces hard compute budgets, silently downgrading a requested model ... or applying rate limits (429s)" — silent downgrade is real (ModelPolicy clamping, ADR-019); hard budget caps and 429s are not implemented.
• site/manifesto.md mirrors both claims.

The cost accumulator meters spend per agent/provider/model but takes no enforcement action.

Fix

Soften the claims to what ships: the proxy meters compute and is the enforcement point for budgets; budget/rate-limit enforcement is roadmap (tracked separately — see the budgets issue under #302). Keep silent model downgrade as a real, shipped claim.

Files to sweep: MANIFESTO.md, site/manifesto.md, site/guide/cllama.md, site/index.md feature cards.

Acceptance

No public doc states budget or rate-limit enforcement as a present-tense capability until it ships.