refactor: Remove RainbowKit and WalletConnect cloud dependencies (EIP-6963 Migration)

[kushbosamiya]

1. Problem

The frontend relies on @rainbow-me/rainbowkit and WalletConnect/Reown infrastructure, which introduces a cloud dependency and a Single Point of Failure (SPOF). This violates the core architectural directive of zero cloud dependencies for wallet connections.

• Specifically, lib/config.ts, providers/providers.tsx, and components/ui/ConnectBtn.tsx are tightly coupled to NEXT_PUBLIC_WALLETCONNECT_PROJECT_ID.
• This introduces external relay servers and potential centralized censorship vectors.

2. Current Behavior

• Reproduction: Connecting a wallet via the UI relies on <RainbowKitProvider> and <ConnectButton.Custom>. Mobile and general connections attempt to ping WalletConnect's relay endpoints.
• Evidence: lib/config.ts currently imports getDefaultConfig and requires a WalletConnect projectId which actively makes network calls to Reown infrastructure upon initialization and connection.
• Comparison: Deleting just the projectId breaks the components. We need a complete, atomic replacement of the connection layer to guarantee pure client-side wallet discovery.

flowchart TD
    %% ===== STYLES (Soft + Minimal) =====
    classDef base fill:#F8FAFC,stroke:#CBD5E1,stroke-width:1.5px,color:#0F172A
    classDef action fill:#E0F2FE,stroke:#7DD3FC,color:#075985
    classDef decision fill:#FEF3C7,stroke:#FCD34D,color:#78350F
    classDef success fill:#ECFDF5,stroke:#86EFAC,color:#065F46
    classDef error fill:#FEE2E2,stroke:#FCA5A5,color:#7F1D1D
    classDef external fill:#F1F5F9,stroke:#CBD5E1,color:#334155

    %% ===== FLOW =====
    A([Open pool page]):::base --> B[Enter amount]:::action

    B --> C{WETH balance sufficient}:::decision

    C -->|Yes| D[Check allowance]:::action
    C -->|No| E[Insufficient balance]:::error

    E --> F[Open Etherscan]:::external
    F --> G[Call WETH deposit]:::external
    G --> H[Return to app]:::external

    H --> B

    D --> I{Allowance sufficient}:::decision

    I -->|Yes| J[Submit buy]:::success
    I -->|No| K[Approve WETH]:::action

    K --> J

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3. Proposed Solution

Migrate to pure wagmi v2 using multiInjectedProviderDiscovery: true (EIP-6963) to allow decentralized, peer-to-peer browser wallet discovery without external APIs.

• Uninstall @rainbow-me/rainbowkit and any @walletconnect/* dependencies.
• Update lib/config.ts to use createConfig from wagmi without the WalletConnect connector.
• Rebuild ConnectBtn.tsx natively using useConnect, useAccount, and useDisconnect to maintain functionality and visual flow.
• Remove NEXT_PUBLIC_WALLETCONNECT_PROJECT_ID from .env.example.

flowchart TD
    %% ===== STYLES =====
    classDef base fill:#F8FAFC,stroke:#CBD5E1,stroke-width:1.5px,color:#0F172A
    classDef action fill:#E0F2FE,stroke:#7DD3FC,color:#075985
    classDef remove fill:#FEE2E2,stroke:#FCA5A5,color:#7F1D1D
    classDef success fill:#ECFDF5,stroke:#86EFAC,color:#065F46

    %% ===== FLOW =====
    A([Start]):::base --> B[Remove WalletConnect + RainbowKit]:::remove
    B --> C[Setup wagmi v2 config]:::action
    C --> D[Enable EIP-6963 discovery]:::action
    D --> E[Build Connect Button using wagmi hooks]:::action
    E --> F[Browser detects wallets]:::base
    F --> G[User connects wallet]:::success
    G --> H([Direct connection established]):::success

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4. Acceptance Criteria

• Wallet connection functions completely client-side with no network calls to *.walletconnect.com or *.reown.com.
• @rainbow-me/rainbowkit package successfully removed from package.json.
• Custom connect button built using wagmi hooks correctly handles connect, network switching, and disconnects.
• No behavioral regressions.
• Verified locally via build/lint/test.

[kushbosamiya]

@Zahnentferner @KanishkSogani could you please assign me!