feat: end-to-end multi-token (SEP-41) deposit support (Closes #255)

[waterWang]

Summary

Implements end-to-end multi-token (SEP-41) deposit support for pools, per issue #255. The contract already exposes set_supported_tokens / get_supported_tokens; this PR wires the token-aware amount maths and activity recording that the deposit flow was missing.

What changed

frontend/lib/deposit-token.ts — new dependency-free pure-logic module (mirroring deposit-calendar.ts / batch-deposit.ts) shared by the deposit UI and API:

• normalizeDecimals / humanToBaseUnits / baseUnitsToHuman / trimHumanAmount — exact human ↔ base-units (stroops) conversion per asset decimals, immune to floating-point error ("0.07" @ 7 decimals → exactly 700000)
• validateTokenSelection — checks a chosen token against the pool's supported set (empty list = unrestricted), with clear per-pool errors
• checkSufficientBalance — validates a human amount against an on-chain base-units balance in the correct unit
• computeDepositFee — treasury + relayer bps fee computed in the settlement token's own unit

frontend/lib/deposit-token.test.ts — 14 unit tests covering decimals conversion, token selection, balance checks and fee maths.

frontend/app/api/pools/deposit/route.ts — token-aware deposit route:

• Accepts optional tokenSymbol, tokenDecimals, tokenAmount
• Validates that tokenAmount has at most the asset's supported precision (rejects e.g. 8 decimals for a 7-decimal asset)
• Records token_amount (token-denominated) alongside amount so deposit history can be broken out by currency
• Describes the activity row with the token symbol for non-XLM currencies

frontend/components/group/group-actions.tsx — passes the pool's tokenSymbol through to the deposit logging route.

frontend/package.json — test:unit includes the new deposit-token.test.ts.

Verification

• 126/126 unit tests pass (14 new + existing suites)
• batch-deposit.test.tsx 12/12, group-actions.test.tsx 8/8 pass
• tsc --noEmit — no new errors from changed files (73 pre-existing unrelated errors untouched)
• ESLint clean on all changed files; Prettier formatted

Closes #255

[Sendi0011]

Coordination: duplicates #257 (both close #255)

Nice implementation — the integer-exact SEP-41 amount maths and the shared deposit-token.ts module are well done. However, this PR and PR #257 both close issue #255 (multi-token SEP-41 deposits) and modify the same core files (app/api/pools/deposit/route.ts, group-actions.tsx, lib/deposit-token.ts, lib/deposit-token.test.ts).

PR #257 is currently the more complete of the two (it adds the supported_tokens DB migration, token-settings UI, tx-retry, and pending-transactions wiring) and is mergeable-clean, while this PR shows dirty (conflicts). To avoid a merge conflict and a double-implementation of the same feature, please coordinate: either rebase and reconcile against #257, or close this PR in favour of #257 (its deposit-token maths can be reused).

No issues with the code itself — happy to approve if this is the one we keep, but only one of the two can merge.