[Feature] Add TVL/balance trend sparkline to pool cards

[grantfox-oss]

Getting Started

1. Fork the repository: https://github.com/JointSave-org/Joint_Save
2. Clone your fork:

   git clone https://github.com/<your-username>/Joint_Save.git
   cd Joint_Save

3. Create a new branch:

   git checkout -b feat/pool-card-trend-sparkline

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Overview

Checked pool-card.tsx and confirmed there's no historical trend visualization at all — just the current balance as a static number. A small sparkline showing the pool's balance trajectory over time would give a much quicker sense of whether a pool is healthy and growing versus stagnant, especially useful on the Explore page when comparing pools.

Requirements

• Periodically snapshot each pool's total balance (a lightweight scheduled job, or piggybacking on an existing activity write) into a new pool_balance_history table
• Add a small sparkline (a tiny inline SVG or a minimal charting library already available in this project, like recharts) to pool-card.tsx showing the last 30 days of balance history
• Should degrade gracefully for pools with little or no history (show a flat line or omit the sparkline entirely rather than a broken/empty chart)
• Keep it lightweight — this is a small visual accent on a card, not a full analytics view

Acceptance Criteria

• Sparkline renders correctly for a pool with real history
• Pools with insufficient history don't show a broken or misleading chart
• No noticeable performance impact on the Explore/My Groups grid when rendering many cards at once
• Snapshot mechanism doesn't add significant load (reasonable interval, e.g. daily)

[Ebenezer199914]

can i work on this issue

[AbuJulaybeeb]

Hi Maintainer, haven reviewed the description of the issue, and well experienced with Js Library,
I would like to hop on the issue and sure to deliver at ETA 2hrs

[grantfox-oss]

🦊 GrantFox — @Ebenezer199914 has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #142)
2. Your PR will be reviewed by the JointSave-org maintainers

Good luck! Track your progress on GrantFox.