feat(mecatui): expose run and team token budgets in embedded configuration

Problem

mecated exposes --max-run-tokens and --max-team-tokens, but the mecatui embedded-server configuration leaves app.Config.MaxRunTokens and app.Config.MaxTeamTokens at their zero values. This makes both budget brakes unlimited in the default local TUI, and there is no operator config-file way to set them.

Desired change

Add operator-tier configuration-file support for the embedded mecatui server per-engine and team-wide token ceilings. The configuration should map through mecatui resolved config into app.Config.MaxRunTokens and app.Config.MaxTeamTokens.

Acceptance criteria

• The operator settings file can configure a positive per-engine run-token ceiling and a positive team-wide token ceiling for embedded mecatui.
• Absent settings retain current behavior: 0 / unlimited.
• Invalid values fail closed or are reported consistently with existing settings parsing conventions.
• The values reach app.Config.MaxRunTokens and app.Config.MaxTeamTokens; the existing inherited/tighten-only budget semantics remain unchanged.
• Configuration precedence and operator-vs-project trust treatment are documented and covered by tests.
• User-facing mecatui documentation explains the settings and their distinction from child per-call max_run_tokens.

Context

Current mecated flags: cmd/mecated/main.go:1417-1418. Mecatui has no corresponding fields/flags and its embeddedConfig does not set the app config values: cmd/mecatui/config.go, cmd/mecatui/main.go (embeddedConfig). The budget behavior itself is already implemented in engine/agent/loop.go (effectiveMaxRunTokens, budgetExhausted) and team supervisor code; this is composition/config plumbing, not new budgeting behavior.