feat: add Jalali (Persian/Shamsi) calendar support with Saturday as week start

[hamedf62]

Description

This PR adds Jalali (Persian/Shamsi) calendar support and Saturday as first day of week to Bulwark Webmail.

What is the Jalali calendar?

The Jalali (also known as Persian or Shamsi) calendar is the official calendar of Iran and Afghanistan. It's a solar calendar with 12 months (Farvardin through Esfand) and is one of the most accurate calendar systems in use today. The week in Iran starts on Saturday (شنبه).

Key Features

1. Automatic calendar switching: When the locale is set to fa (Persian/Farsi), the calendar automatically displays Jalali months and dates
2. Saturday as week start: FirstDayOfWeek setting now supports Saturday (6) alongside Sunday (0) and Monday (1)
3. Display-only conversion: All internal date handling remains Gregorian (ISO 8601) for JMAP protocol compatibility — Jalali conversion happens only at the UI layer
4. Full Persian locale: Includes complete fa translations for the entire UI

Changes

New Files

• lib/jalali-utils.ts — Gregorian ↔ Jalali conversion utilities using jalaali-js
• hooks/use-calendar-locale.ts — Unified calendar locale hook abstracting Gregorian/Jalali differences
• locales/fa/common.json — Full Persian (Farsi) locale with ~3200 translations

Modified Files

File	Change
stores/settings-store.ts	FirstDayOfWeek type expanded to 0 | 1 | 6
components/settings/language-settings.tsx	Added Saturday to first-day picker
components/calendar/calendar-month-view.tsx	Uses useCalendarLocale for Jalali-aware rendering
components/calendar/calendar-week-view.tsx	Supports weekStartsOn: 6
components/calendar/mini-calendar.tsx	Jalali month grid, headers, month picker
components/calendar/calendar-toolbar.tsx	Jalali month/year/week labels
hooks/use-format-event-date.ts	Shows Jalali dates for fa locale
package.json	Added jalaali-js dependency
All 20 locales/*/common.json	Added Jalali month name keys

How It Works

┌──────────────────────────────────────────────────┐
│                    UI Layer                       │
│  ┌────────────────────┐  ┌────────────────────┐  │
│  │  Gregorian (en)    │  │  Jalali (fa)       │  │
│  │  "June 2026"       │  │  "تیر ۱۴۰۵"        │  │
│  │  Mon Tue Wed ...   │  │  ش  ی  د  س ...    │  │
│  └────────┬───────────┘  └────────┬───────────┘  │
│           │                       │               │
│           │    useCalendarLocale() │               │
│           │                       │               │
│  ┌────────┴───────────────────────┴───────────┐  │
│  │          Internal Date (Gregorian)          │  │
│  │          ISO 8601 / JMAP compatible         │  │
│  └─────────────────────────────────────────────┘  │
└──────────────────────────────────────────────────┘

Testing

• ✅ TypeScript compilation: no new errors
• ✅ All calendar views render correctly with Saturday-first ordering
• ✅ Jalali month grid shows correct day counts (including leap years)
• ✅ Today detection works for both calendars
• ✅ Month/year navigation works correctly
• ✅ Event date formatting shows Jalali dates for fa locale
• ✅ Week numbers display correctly for all week-start options

Known Interactions

• PR feat(templates): rich text editor + inline images in email templates #462 (template rich editor) adds settings.templates.image_too_large to all 19 existing locale files. Our fa locale already includes this key with a Persian translation. The 19 shared locale files will have a trivial 2-line merge conflict if both PRs merge around the same time — the resolution is to apply both additions.
• PR feat(compose): auto-detect RTL text direction while writing #469 (RTL auto-detect) is fully complementary — no file conflicts, and it enhances the Persian user experience alongside this PR.

Notes for Reviewers

• The fa locale file is included as a new addition to support Persian language users
• jalaali-js is a lightweight (no dependencies), well-maintained library for calendar conversion
• The hook-based architecture (useCalendarLocale) keeps the calendar system abstraction clean and makes it easy to add support for other non-Gregorian calendars in the future

[shukiv]

Ahalan wasahalan :-)

[hamedf62]

Alaikum Salam