Implement Full Scrollable Payment Timeline for Contract Payment Flow [Flutter] #57
Description
Build the complete scrollable timeline for the Contract Payment flow, covering the full multi-cycle lifecycle: Contract cycle completed → Client approved contract cycle → Invoice created for cycle → Client payment confirmed → Payment processed → Funds received. Additional states include "Awaiting client approval", "Pending payment confirmation", "Client payment overdue", and "Milestone completion submitted". Each step follows the same vertical stepper pattern as the Invoice timeline but includes Contract-specific steps and milestone tracking. Multiple recurring cycles should be visually grouped and the timeline must scroll through all cycles.
Acceptance Criteria:
- Full contract timeline renders as a vertical scrollable stepper
- Contract-specific steps render correctly: cycle completion, client approval, milestone submission
- "Awaiting client approval" and "Pending payment confirmation" steps appear with outlined indicators when not yet completed
- "Client payment overdue" step renders with appropriate visual treatment
- "Milestone completion submitted" / "Milestones completed" steps are included
- Repeating contract cycles are visually grouped or separated
- Inline prompts (e.g., "Prove your client payment") are tappable
- Timeline scrolls smoothly and handles all step variants without layout issues