Clarify cost display as API-rate estimate

[yashiels]

Summary

• Add persistent hint below cost figures: "Estimated from local logs · may differ from your bill"
• Change "Cost" section header to "Cost (estimated)" with localization (en, pt-BR, zh-Hans)
• Update CLI output from "(local)" to "(API-rate estimate)" with footer disclaimer
• Update chart footer to "Est. total (30d)" with truncation safety

Closes #549.

Context

Users on flat-rate subscriptions (Claude Max, Codex Pro) panic when they see dollar amounts computed from local logs at API pricing rates. The hint clarifies these are estimates, not invoiced charges. The wording is universally accurate — API users also benefit since local log estimates may differ from actual invoices due to caching, batching, and discount tiers.

Prior PR #464 was closed as too large (subscription detection + settings toggle). This PR follows the guidance to "reopen as a fresh, smaller PR" — no conditional logic, no new settings, just clear labeling.

Changes

File	Change
UsageFormatter.swift	Add costEstimateHint public constant
MenuCardView.swift	Assign hint to hintLine, change 2× Text("Cost") → localized key
CostHistoryChartMenuView.swift	Footer "Est. total (30d)" + lineLimit(1) + truncationMode(.head)
CLICostCommand.swift	Header "(API-rate estimate)" + footer disclaimer
en/pt-BR/zh-Hans .strings	Add cost_header_estimated + cost_estimate_hint keys
CLICostTests.swift	Update CLI assertion + add hint stability test

Validation

• swift build — clean (942 targets)
• swift test --filter CLICostTests — all 5 tests pass (including updated + new tests)
• Tested locally on macOS — built from source and verified UI + CLI
• Translations are machine-generated for pt-BR and zh-Hans — happy to take corrections

Screenshots

Menu bar (dark mode)

Before: Header says "Cost", no hint line
After: Header says "Cost (estimated)", hint line reads "Estimated from local logs · may differ from your bill"

CLI output

Claude Cost (API-rate estimate)
Today: $113.58 · 154M tokens
Last 30 days: $1,097.61 · 1.3B tokens
Estimated from local logs · may differ from your bill

Deferred (separate PRs)

• Widget labels → "Today est." / "30d est." (compact widget layout requires different approach)
• Preferences subtitle wording update

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[yashiels]

Verified locally — menu bar + CLI (dark mode, macOS 15.3)

Built from source and tested all changes:

• Header: "Cost (estimated)" ✓
• Hint line: "Estimated from local logs · may differ from your bill" in secondary/grey ✓
• CLI: "Claude Cost (API-rate estimate)" with footer disclaimer ✓
• Chart footer: "Est. total (30d)" ✓

CLI output:

Claude Cost (API-rate estimate)
Today: $113.58 · 154M tokens
Last 30 days: $1,097.61 · 1.3B tokens
Estimated from local logs · may differ from your bill

[steipete]

Thanks @yashiels. Landed a maintainer version on main in 73c8209, with your attribution preserved in the commit.

I kept the intent and adjusted it against current main:

• Menu/card/chart/CLI labels now say the totals are API-rate/local-log estimates.
• Added localized strings for the new menu labels.
• Updated CLI cost tests for the estimate header and hint.

Verified with swift test and make check. Closing this PR because main now contains the shipped version.