fix: prevent Chrome auto-translate from crashing onboarding (#65)

* fix: prevent Chrome auto-translate from crashing React during onboarding

Chrome auto-translate modifies DOM text nodes when it detects a Swedish
page (lang="sv") in a browser set to English. React does not expect
external DOM mutations and throws, crashing the entire component tree
into global-error.tsx on every step transition.

Add translate="no" and <meta name="google" content="notranslate"> to
suppress browser translation. Also fix timezone-unsafe date parsing in
fiscal period validation (new Date("YYYY-MM-DD") + getDate() returns
local-timezone values, shifting dates by -1 day in Western timezones).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: add notranslate meta tag to global-error.tsx for consistency

Per review feedback — global-error.tsx renders its own <html> document,
so it needs the same <meta name="google" content="notranslate"> tag as
layout.tsx to fully suppress Chrome translation on error pages.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/bookkeeping/validate-period-duration.ts

@@ -4,14 +4,25 @@
  * Normal ongoing periods are 12 months.
  */
 
+/**
+ * Parse a YYYY-MM-DD string into numeric parts without timezone issues.
+ * Using new Date(dateStr) is unsafe because it creates UTC midnight,
+ * but getDate()/getMonth()/getFullYear() return local-timezone values —
+ * shifting the date by -1 day in Western timezones.
+ */
+export function parseDateParts(dateStr: string): { year: number; month: number; day: number } {
+  const [year, month, day] = dateStr.split('-').map(Number)
+  return { year, month, day }
+}
+
 /**
  * Calculate the number of months between two dates (inclusive of partial months).
  * Assumes start is 1st of month and end is last of month.
  */
 export function monthsBetween(start: string, end: string): number {
-  const s = new Date(start)
-  const e = new Date(end)
-  return (e.getFullYear() - s.getFullYear()) * 12 + (e.getMonth() - s.getMonth()) + 1
+  const s = parseDateParts(start)
+  const e = parseDateParts(end)
+  return (e.year - s.year) * 12 + (e.month - s.month) + 1
 }
 
 /**
@@ -19,22 +30,23 @@ export function monthsBetween(start: string, end: string): number {
  * Returns null if valid, or an error message string if invalid.
  */
 export function validatePeriodDuration(start: string, end: string): string | null {
-  const startDate = new Date(start)
-  const endDate = new Date(end)
+  const startParts = parseDateParts(start)
+  const endParts = parseDateParts(end)
 
-  // end must be after start
-  if (endDate <= startDate) {
+  // end must be after start (YYYY-MM-DD strings are lexicographically orderable)
+  if (end <= start) {
     return 'Period end must be after period start'
   }
 
   // start must be 1st of month
-  if (startDate.getDate() !== 1) {
+  if (startParts.day !== 1) {
     return 'Period start must be the 1st of a month'
   }
 
   // end must be last day of month
-  const lastDayOfEndMonth = new Date(endDate.getFullYear(), endDate.getMonth() + 1, 0).getDate()
-  if (endDate.getDate() !== lastDayOfEndMonth) {
+  // new Date(year, 1-indexed-month, 0) gives the last day of that month
+  const lastDayOfEndMonth = new Date(endParts.year, endParts.month, 0).getDate()
+  if (endParts.day !== lastDayOfEndMonth) {
     return 'Period end must be the last day of a month'
   }