chore(android): bump app version to 1.0.6

[SebastianBoehler]

Summary

• bump Flutter version name from 1.0.0 to 1.0.6, following the existing v1.0.5 release
• bump Android version code from 6 to 7 for the next Google Play testing upload

Verification

• confirmed the Flutter Android Gradle config consumes flutter.versionCode and flutter.versionName
• confirmed release CI will create the new v1.0.6 tag rather than clobber an existing release
• git diff --check
• full Flutter build not run locally because Flutter is unavailable in the gateway image; PR CI runs analysis, tests, and Android packaging

Release note

Google Play requires the uploaded artifact version code to exceed every code already uploaded to any testing or production track. If Play Console already contains a manually overridden code above 6, update this PR to a higher build number before upload.

[SebastianBoehler]

Closing as requested. Note for the next Play upload: versionCode 6 can only be uploaded once; if code 6 is already present on any Play track, the next artifact must use 7 or higher.