#7006 iOS: add in-app share diagnostics

Fixes #5515

Summary

• Adds a release-safe mobile diagnostics report builder with secret scrubbing, app/device metadata, auth/connection state, event logs, debug log, and recent OSLog lines.
• Wires Share Diagnostics into the iOS workspace detail menu with Copy and ShareLink actions.
• Injects diagnostics logs in Release/TestFlight and records redacted auth/connection transitions.

Validation

• git diff --check
• python3 -m json.tool ios/cmux/Resources/Localizable.xcstrings >/dev/null
• python3 scripts/check-workspace-package-groups.py --check
• Localization audit: added en/ja entries for mobile.diagnostics.close/copy/share/shareAction and checked both locales are present.

Local dev builds and xcodebuild were intentionally not run per issue instructions.

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Summary by cubic

Adds in‑app Share Diagnostics on iOS so users can copy or share a redacted report from the Workspace menu. Tightens privacy and improves support/triage for #5515.

• New Features

  • Introduces CmuxMobileDiagnostics: secret scrubber, report builder, store‑scoped in‑app event log, and a current‑process OSLog reader that omits message bodies and preserves an “OSLog unavailable” status.
  • Adds a “Share Diagnostics” sheet with selectable text, Copy, and Share; shows app/device info, auth (with last display‑safe error), connection (host/last error), in‑app events, debug‑log line count, and OSLog count/status; omits the process‑wide structured log for account‑scoped privacy; adds en/ja strings.
  • Builds a structured DiagnosticLog for all builds to stamp feedback; it remains private in Release and is exportable only on DEBUG.

• Bug Fixes

  • Records display‑safe auth failures via AuthCoordinator.lastAuthError across send/verify code, OAuth, password sign‑in, token read/refresh, and offline checks; clears on successful sign‑in.
  • Protects shared‑device privacy and stability: blanks host before disconnect, scrubs and retains lastConnectionError, scopes the diagnostics event log to the shell store and swaps in a fresh instance on sign‑out to avoid races and cross‑account leakage, and cancels report work if the sheet is dismissed; gates structured diagnostic‑log export to DEBUG in privileged feedback.
  • Improves Xcode 16 compatibility with nonisolated loggers, a Sendable notification‑status read, and compiler‑guarded iOS 26 glass APIs.

Summary by CodeRabbit

• New Features
  • Added an in-app iOS “Share Diagnostics” sheet with a selectable, copy/shareable report and automatic secret redaction.
  • The report now includes app metadata, auth/connection status, in-app events, structured diagnostics events, and recent OS log entries.
  • Added diagnostics event logging for sign-in/out and connection error changes.
• Bug Fixes
  • Improved authentication error tracking so the most recent display-safe auth failure is consistently captured.
  • Hardened chat UI keyboard handling and iOS 26-related scrolling/glass styling across compiler versions.
• Tests
  • Added/updated unit tests for diagnostics report formatting/redaction and auth offline/unauthorized error assertions.