fix(rtl): auto-detect text direction in read, print and plain-text views

[shukiv]

Problem

The reader renders message bodies with the UI's direction, not the message's. With an RTL UI (Hebrew/Arabic/Persian), an English email is right-aligned; with an LTR UI, a Hebrew email is left-aligned. Mixed-language mail is wrong either way.

Fix

Add dir="auto" in the three places a message body is rendered:

• the sandboxed HTML iframe body
• the print view body
• the plain-text render container

auto resolves direction per block from its first strong character, so each paragraph aligns by its own content — an English paragraph stays LTR even inside an RTL UI, and vice-versa. Mixed-language messages render each block correctly.

Three attributes, no logic or dependency changes; LTR-only mail is unaffected (auto resolves to LTR).

Testing

• Hebrew email in an English UI → right-aligned ✅
• English email in a Hebrew UI → left-aligned ✅
• Mixed Hebrew/English message → each paragraph aligned by its own content ✅
• Plain-text and print views match the HTML view ✅
• tsc clean; lint clean (no new warnings)