Add native push notifications with reply actions, content preview, and configurable gateway

[eleboucher]

Description

Reply actions (#1209)

• Inline reply from OS notifications (Android, iOS, desktop)
• Action types registered in tauri.conf.json (sable-message / sable-reply)
• Reply queue with dedup and expiry (nativeNotificationReplies.ts)
• NativeNotificationActionRouting component wired into ClientNonUIFeatures

Content preview (#1182)

• Rich push payloads enabled by default (useRichPushPayloads)
• Fetch + decrypt event when not in local timeline (encrypted rooms)
• largeBody for single-message BigTextStyle (expanded view shows body)
• Sender name fallback for DMs when room name is missing

Configurable gateway URL (#1183)

• pushNotifyUrlOverride setting
• PushPusherConfig.ts helper for URL resolution + payload format

Distributor timeout (#1176)

• Bumps tauri-plugin-notifications to e7a8796 (fixes 2+ distributor selection + native warm-path notifications)"

Fixes #1209 #1183 #1182 #1176

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

AI disclosure:

• Partially AI assisted (clarify which code was AI assisted and briefly explain what it does).
• Fully AI generated (explain what all the generated code does in moderate detail).