docs: map SDK v2 methods to the network vault contract

[Agbasimere]

Summary

• Rewrite docs/sdk-contract-interface.md as the SDK v2 to Network vault bridge: read/write method mapping, argument order, amount formatting, and event topics.
• Document current gaps (wrong read symbols, no get_info, pending vs claimable rewards, event name mismatches).
• Repair vault test helpers so setup / setup_uninitialized compile after overlapping PRs.

Test plan

• cargo fmt --all -- --check
• cargo check --workspace --all-targets
• cargo test --workspace --all-targets
• cargo clippy --workspace --all-targets -- -D warnings
• Confirm the mapping against packages/core/src/contracts/vault.ts in axionvera-sdk
• Confirm event topics ("vault", "deposit"|"withdraw"|"claim") against contracts/vault-contract/src/lib.rs

Closes #339

[El-swaggerito]

\nGitHub has not finished calculating whether this PR can be merged cleanly.\n\nThe auto-merge automation will skip this PR for now. Re-run the automation later.