Vault: read-only API completeness (`get_meta`, `balance`, `get_max_deduct`, etc.)

[greatest0fallt1me]

Description

Ensure documented view functions exist, return stable types for SDK consumers, and fail consistently if uninitialized.

Requirements and context

• Views must not mutate storage.
• Align naming with README and backend expectations.

Suggested execution

• Fork the repo and create a branch: git checkout -b chore/vault-read-api
• Implement changes in the Callora-Contracts Soroban workspace (contracts/*/src/).
• Run cargo fmt, cargo clippy --all-targets --all-features -- -D warnings, and cargo test from the workspace root.
• For WASM release builds: cargo build --target wasm32-unknown-unknown --release -p callora-vault (adjust -p if the crate name differs).

Deliverables

• lib.rs + test.rs per view.
• README "What's included" sync.

Test and commit

• Run tests and ./scripts/coverage.sh (or cargo tarpaulin per tarpaulin.toml).
• Cover edge cases; include summarized test output and brief security notes in the PR description.

Example commit message

docs(vault): align read-only API surface

Guidelines

• Minimum 95% line coverage for touched crates (workspace policy).
• Clear documentation (Rust /// on public items where applicable; repo markdown as needed).
• Timeframe: 96 hours from assignment unless agreed otherwise.

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[DavisVT]

@DavisVT has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

pls assign this issue to me

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[hakymulla]

@hakymulla has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

I'd like to apply for this issue. I have open source experience on the stellar ecosystem.

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