Replace evolution iteration limit with token budget

[cursor]

Summary

• Adds a configurable maxTokenBudget preference and CLI flag for evolutions.
• Stops evolution at the next loop pause when provider-reported token usage reaches the budget, while keeping build-attempt ceilings independent.
• Replaces the Settings “Max Iterations” control with “Token Budget” and shows live cumulative token spend in the evolution progress overlay.
• Keeps the legacy iteration setting only as an internal fallback for providers that do not report token usage.

Resolves ENG-525

Test Plan

• bun -F native lint
• bun -F native build
• bun -F native test:unit
• bun -F native test:storybook -- "src/components/widget/settings/ai-models-tab.stories.tsx" "src/components/widget/overlays/evolve-progress.stories.tsx"
• bun -F native test:storybook -- "src/components/widget/widget.stories.tsx"

Notes:

• cargo +stable check --locked --manifest-path apps/native/src-tauri/Cargo.toml and cargo +stable run --locked --example specta_gen_ts are blocked in this Linux runner by missing system library gdk-3.0.
• The full storybook suite still has unrelated snapshot mismatches in rebuild-overlay-panel.stories.tsx and file-view.stories.tsx; changed PR story surfaces pass.

Docs

• Docs updated (companion PR in darkmatter/nixmac-web: #___)
• No docs update needed

  

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[github-actions]

	Warnings
⚠️	PR is marked WIP / draft — do not merge until ready for review.
⚠️	Please assign this PR to someone (usually yourself).

	Messages
📖	No docs update needed — acknowledged.

📋 PR Overview

Lines changed	355 (+254 / -101)
Files	0 added, 21 modified, 0 deleted
Draft / WIP	yes
Has Test Plan	yes
New UI components	no
New Storybook stories	no
New Rust modules	no
New TS source files	no
New tests	no
package.json touched	no
Cargo.toml touched	no
Infra / CI touched	no

🔬 Coverage

Report	Lines	Statements	Functions	Branches
apps/native/coverage/coverage-summary.json	17.9%	17.9%	30.8%	54.1%

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