feat: DM UX improvements

[barrydeen]

Summary

• Auth persistence — relay AUTH approvals are now saved to SharedPreferences (keyed per user), so the approval dialog only appears once per relay, not on every message or app restart
• Keyboard capitalisation — DM message input now auto-capitalises the first letter of each sentence
• Action bar mirroring — icon order in the action bar is reversed for received bubbles so the expand arrow is always adjacent to the bubble edge on both sides
• Telegram-style reaction pills — reactions moved from plain text into compact pills inside the bubble, showing the emoji alongside stacked small avatars of the reactors

Test plan

• Send a DM to an AUTH-required relay, approve once — confirm the dialog does not reappear on subsequent messages or after restarting the app
• Open DM compose input and verify the keyboard auto-capitalises sentence starts
• Check sent and received bubbles — expand arrow should be closest to the bubble on both sides
• React to a DM message and confirm the pill appears inside the bubble with the emoji and reactor avatar

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