Bump flutter_bugfender to ^5.0.0

[PiotrRogulski]

Summary

• Bump flutter_bugfender dependency from ^4.0.0 to ^5.0.0
• Bump package version 5.0.0+1 → 6.0.0, following this repo's convention of bumping the major version alongside flutter_bugfender major bumps
• Add a 6.0.0 CHANGELOG entry

flutter_bugfender 5.0.0 adds new network-logging APIs and updates native SDKs, but keeps init, fatal/warn/info/trace, and the setDevice*/removeDeviceKey methods unchanged with the same signatures used here, so no code changes were needed in lib/. Its SDK constraint (dart >=3.3.0 <4.0.0) is already satisfied by this package's environment settings.

Test plan

• CI (flutter analyze across Flutter 3.19.0 / 3.24.3 / 3.38.5) passes

---

Generated by Claude Code