feat(faucet): add validated token catalog and funding strategies

[ameya-deshmukh]

Sandbox integrations may use different settlement tokens while Base funding currently has one USDC identity. This first slice adds a validated token catalog and explicit funding strategies, preserving the default identity and existing endpoints.

Closes https://linear.app/seismic-systems/issue/SEI-662

• Load additional tokens from a deployment-managed JSON file selected by INTERNAL_FUNDING_BASE_TOKEN_CATALOG_FILE; include a generic two-token example and ignore the local deployment catalog.
• Validate the file at startup, including contract uniqueness, decimals, budgets, and bounded mint calls. An unset path preserves defaults; unreadable or invalid configuration makes Base unavailable with a diagnostic. Restart to apply catalog edits.
• Plan caller-only whole-token minting (tested with six decimals and a 100-token per-call limit); report manual funding when inventory cannot replenish automatically.
• Keep additional tokens inactive until the follow-up adds contract-aware requests, execution, and durable retry recovery.

Before

flowchart LR
  A[Base config] --> B[One default USDC identity]
  B --> C[Existing funding endpoints]

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After

flowchart LR
  A[Existing Base config] --> B[Legacy default USDC]
  C[Optional token catalog JSON file] --> D[Validated catalog]
  B --> D
  D --> E{Funding strategy}
  E --> F[Manual inventory]
  E --> G[Bounded whole-token mint plan]
  G -. Future runtime PR .-> H[Persist, submit, confirm, then transfer]

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Validation: Rust 1.88 workspace fmt, clippy with warnings denied, locked tests (including Redis integration), and release build passed. No on-chain transaction submitted.

This foundation can merge independently. Contract-aware endpoints, mint execution, and durable retry recovery will follow in a separate PR. Additional settlement tokens remain inactive until that runtime support is deployed.

[linear-code]

SEI-662