feat(vault): track deployed vs idle assets via derived getters

[davidmaronio]

Summary

Adds read-only getters that split the vault's value into idle (held directly by the contract) vs deployed (supplied to an external protocol), so liquidity management and audits no longer have to infer the split from TotalDeposits/TotalAssets.

• get_idle_balance() — USDC held directly by the vault contract.
• get_deployed_assets() — USDC currently supplied to the active protocol (Blend/DEX); returns 0 when CurrentProtocol is "none".
• get_asset_breakdown() — returns (idle, deployed) in a single call for dashboards/agents.

All three are derived read-only getters (no new storage), guarded by require_initialized, and follow the existing getter + doc-comment conventions.

Acceptance criteria

• Derived getter(s) for deployed vs idle — get_idle_balance / get_deployed_assets / get_asset_breakdown.
• Tests after rebalance show the correct split — tests/test_asset_split.rs (4 tests: idle == deposit & deployed == 0 before rebalance; idle → 0 & deployed == deposit after rebalancing into Blend; get_asset_breakdown matches the individual getters).
• ARCHITECTURE.md updated with an "Idle vs Deployed Asset Tracking" section, including the relationship to TotalAssets.

Generated artifacts

Regenerated contract-spec.json and packages/vault-client/src/generated/vault.ts, and registered the new functions in scripts/generate-spec.py (same pattern as the other query functions).

Verification

• cargo test test_asset_split → 4 passed; 0 failed.
• Change is purely additive to lib.rs (no existing lines modified).
• scripts/check-no-bare-panic.sh passes.

Note on pre-existing CI state

A few items are pre-existing on main and unrelated to this change: validate-spec.py already reports error-shape drift for VaultError codes 28–48 (identical count with and without this PR — no new drift introduced), and test_rebalance_cooldown / test_strategy_switch_low_liquidity / test_ttl already fail locally. Happy to address those separately if wanted.

Closes #321

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