Redesign repeater markers as cleaner pills

[Bjorkan]

AI disclosure: This entire pull request was written by OpenAI GPT-5.6 Sol High.

Summary

• Replaces the repeater marker's left status bar and glow with a continuous status-coloured border.
• Uses a consistent dark body, capsule shape, height, and centred label across all repeater states.
• Keeps observer indicators out of scope because the Flutter app does not currently expose observer state.
• Updates the map legend, marker documentation, and rendering tests to match the new design.

Preview

Testing

• flutter analyze --no-pub
• flutter test --no-pub — 2180 passed, 1 skipped

[Bjorkan]

CI failure is unrelated to this PR. I reproduced the exact format check on both the PR base (dev at b22a950) and this branch: both report the same 99 files, with no differences between the two lists. The Flutter 3.47.5/Dart formatter baseline on dev therefore needs to be fixed separately; formatting all 99 files here would add substantial unrelated churn to this marker-only PR.