feat(usage): add hide-when-zero state to usage widgets and reset timers

[tough-griff]

Closes #598

Adds an opt-in zero hideable state (via the existing (h)ide… checklist) to the usage widgets and reset timers.

Changes

• Session / Weekly / Weekly Sonnet / Weekly Opus / Weekly Fable Usage: hide when the raw usage is 0%, regardless of the used/remaining toggle. Implemented once in renderUsagePercentWidgetValue.
• Block Reset Timer / Weekly Reset Timer: hide when the period's usage is 0% and no reset time was reported. The reset-time guard matters because a null API bucket pins usage to 0% even when limits[] still supplies a live window (Weekly session usage not updating after fable-only usage added #503), so without it the option would hide a valid countdown on migrated accounts.
• Extra Usage Used / Utilization: hide at $0 spent / 0%. Extra Usage Remaining is deliberately left out.
• Migrations: the v3 → v4 hide-flag rule for Extra Usage Used/Utilization now lists zero, so a hand-written hide list keeps it.
• Docs: docs/USAGE.md hide-state list updated.

Testing

• New cases in the shared usage-percent suite (covers all five usage widgets), both timer tests (including the reset-time guard), and both Extra Usage tests
• bun test and bun run lint pass
• Manually verified against an Enterprise account (every window null) and the example payload

Enterprise account, same line as in #598. Before (config in #598: Session Usage, Weekly Usage and both reset timers on hide: no-data; the Extra Usage widgets on disabled,no-data):

$XYZ ▓▓▓▓▓▓▓▓▓░ 85.1% | 0% 2h5m | 0%

After (zero added to every widget; the Extra Usage widgets stay visible because spend is non-zero):

$XYZ ▓▓▓▓▓▓▓▓▓░ 85.4%

Widget config for the after line

[
  {
    "id": "fb09dd02-a41b-4172-bfdf-4dd7e329b8a7",
    "type": "extra-usage-used",
    "color": "ansi256:11",
    "numberFormat": {
      "style": "compact"
    },
    "rawValue": true,
    "metadata": {
      "hide": "disabled,no-data,zero"
    }
  },
  {
    "id": "9fdb44e0-25bf-44ac-b943-a34f1b377d18",
    "type": "separator",
    "character": " "
  },
  {
    "id": "351546ed-1c7c-4663-8c2a-cf7ca36443b7",
    "type": "extra-usage-utilization",
    "color": "ansi256:11",
    "numberFormat": {
      "style": "compact"
    },
    "rawValue": true,
    "metadata": {
      "display": "slider",
      "invert": "false",
      "hide": "disabled,no-data,zero"
    }
  },
  {
    "id": "7b2987cb-1c37-4f4c-bce6-4adb6d482626",
    "type": "separator",
    "color": "ansi256:7",
    "dim": true
  },
  {
    "id": "b125133a-d2da-4254-955e-ad9bfa5a3487",
    "type": "session-usage",
    "color": "ansi256:80",
    "numberFormat": {
      "style": "compact"
    },
    "rawValue": true,
    "metadata": {
      "invert": "false",
      "display": "time",
      "hide": "no-data,zero"
    }
  },
  {
    "id": "52245476-8615-43c9-8db5-7fd37c45139c",
    "type": "separator",
    "character": " "
  },
  {
    "id": "6fa9558a-8a03-442c-bfef-dfb5854cba65",
    "type": "reset-timer",
    "color": "ansi256:80",
    "dim": true,
    "numberFormat": {
      "style": "compact"
    },
    "rawValue": true,
    "metadata": {
      "display": "time",
      "compact": "true",
      "absolute": "false",
      "hide": "no-data,zero"
    }
  },
  {
    "id": "d7a551fb-4953-44bd-8448-ecaecacf9668",
    "type": "separator",
    "color": "ansi256:7",
    "dim": true
  },
  {
    "id": "a73d2332-9fbb-48f9-abc5-02d4561157ca",
    "type": "weekly-usage",
    "color": "ansi256:81",
    "numberFormat": {
      "style": "compact"
    },
    "rawValue": true,
    "metadata": {
      "display": "time",
      "invert": "false",
      "hide": "no-data,zero"
    }
  },
  {
    "id": "1df9ff5e-64a3-41ad-8f97-d45367ba35ee",
    "type": "separator",
    "character": " "
  },
  {
    "id": "1a69f9af-0275-40f5-8521-af07f0e8940b",
    "type": "weekly-reset-timer",
    "color": "ansi256:81",
    "dim": true,
    "numberFormat": {
      "style": "compact"
    },
    "rawValue": true,
    "metadata": {
      "display": "time",
      "compact": "true",
      "hours": "false",
      "hide": "no-data,zero"
    }
  }
]

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