Export logs as .tsv file for easier sharing with support

[thibistaken]

Currently, sharing logs from the app uses copy-paste which is impractical for large log files. Logs are often too large for Slack and support agents have to manually paste them into Google Docs then export as PDF. The attach-log button in support chat also fails when the log file is too large (mainly on iOS where there is no periodic log trimming like Android).

User stories

• As a user experiencing issues, I want to export my logs as a .txt file with one tap, so I can easily share it with support via any app
• As a support agent, I want users to send a complete log file, so I can diagnose issues without back-and-forth

Current behavior

• Logs screen only offers copy-to-clipboard / share as text
• Large logs exceed clipboard and Slack limits
• iOS logs grow unbounded (no periodic trimming like Android)
• Support chat log attachment fails on large files

Expected behavior

• "Export logs" button writes logs to a .txt file on the device
• File can be shared via the OS share sheet to any app (email, Signal, Slack, etc.)

Acceptance criteria

• Export button on the logs screen saves a .txt file
• File triggers the OS share sheet for sharing to other apps
• Works on both iOS and Android
• Handles large log files without crashing
• iOS: add periodic log trimming to match Android behavior

Test cases

• Small log file (<1MB): exports and shares successfully
• Large log file (>10MB): exports without crash, file is shareable
• iOS: log file size stays manageable over time with trimming
• Android: existing log trimming still works
• Share sheet opens with correct .txt file attachment

[BBTMGIT]

Please can we get thsi soon.