fix(plan): resolve type errors in plan summary and isActivePlan guard

Two pre-existing type errors surfaced during the rebase against main:

1. JsonPlanSummary.id was hardcoded to four plan ids, but PlanId now
   includes 'none' (PLAN_IDS was extended when 'codeburn plan clear'
   was added). toJsonPlanSummary only runs for active plans at runtime,
   but the static type still had to be widened. Use PlanId directly
   instead of the hand-rolled union.

2. isActivePlan used Boolean(plan) as the nullish guard, which doesn't
   narrow plan's type in TypeScript. Switch to an explicit
   'plan !== undefined' so the subsequent .id and .monthlyUsd accesses
   type-check.

npx tsc --noEmit is now clean; all 285 tests still pass.

Author: tmchow

src/cli.ts

@@ -15,7 +15,7 @@ import { parseDateRangeFlags } from './cli-date.js'
 import { runOptimize, scanAndDetect } from './optimize.js'
 import { renderCompare } from './compare.js'
 import { getAllProviders } from './providers/index.js'
-import { clearPlan, readConfig, readPlan, saveConfig, savePlan, getConfigFilePath } from './config.js'
+import { clearPlan, readConfig, readPlan, saveConfig, savePlan, getConfigFilePath, type PlanId } from './config.js'
 import { clampResetDay, getPlanUsageOrNull, type PlanUsage } from './plan-usage.js'
 import { getPresetPlan, isPlanId, isPlanProvider, planDisplayName } from './plans.js'
 import { createRequire } from 'node:module'
@@ -95,7 +95,7 @@ function parseInteger(value: string): number {
 }
 
 type JsonPlanSummary = {
-  id: 'claude-pro' | 'claude-max' | 'cursor-pro' | 'custom'
+  id: PlanId
   budget: number
   spent: number
   percentUsed: number

src/plan-usage.ts

@@ -144,5 +144,5 @@ export async function getPlanUsageOrNull(today = new Date()): Promise<PlanUsage
 }
 
 export function isActivePlan(plan: Plan | undefined): plan is Plan {
-  return Boolean(plan) && plan.id !== 'none' && Number.isFinite(plan.monthlyUsd) && plan.monthlyUsd > 0
+  return plan !== undefined && plan.id !== 'none' && Number.isFinite(plan.monthlyUsd) && plan.monthlyUsd > 0
 }