Fix onboarding weight validation text and negative profile values

[LarytheLord]

Summary

Fixes the onboarding weight validation message and prevents negative values in profile height/weight pickers.

Closes #288
Closes #216
Closes #217

Changes

• onboarding_second_page_body.dart
  • Fixed validateWeight() to return onboardingWrongWeightLabel instead of onboardingWrongHeightLabel.
• set_height_dialog.dart
  • Added lower-bound clamping for picker minimum value (>= 1) so users cannot scroll into negative heights.
  • Added confirmation-time guard to ensure returned value respects the same lower bound.
• set_weight_dialog.dart
  • Added lower-bound clamping for picker minimum value (>= 1) so users cannot scroll into negative weights.
  • Added confirmation-time guard to ensure returned value respects the same lower bound.

Notes

I could not run Flutter tests in this environment because flutter/dart are not installed here.

[LarytheLord]

Pushed a technical follow-up in commit 2e9d76d to make this PR easier to maintain and safer.

• extracted profile height/weight picker bound and clamp logic into a shared utility (profile_picker_bounds.dart)
• updated both set-height and set-weight dialogs to use the shared functions
• added focused unit tests covering min/max range behavior and lower-bound clamping (profile_picker_bounds_test.dart)

This keeps the original bug fixes intact while adding regression coverage for the boundary logic.