fix(v2): require minimum resolution bond on registration top-ups

[s6pa1rta3n-lab]

Summary

Closes #155

This PR addresses an economic vulnerability where callers could submit cheap dust top-ups (e.g. 1 unit) during the anti-snipe extension window to repeatedly extend the registration deadline up to the hard deadline at minimal cost.

Root Cause & Changes

Previously, register only checked policy.min_resolution_bond on first-time registrations in the match &existing { None => ... } branch. Top-up deposits had no minimum amount constraint, allowing 1-unit top-ups to qualify as late deposits and extend registration_deadline.

• Enforce Minimum Bond on All Deposits (contracts/tholos-v2/src/lib.rs):
  • Moved the amount < assertion.policy.min_resolution_bond check to the top of register, returning Error::BelowMinimumResolutionBond before any storage reads/mutations or deadline extension evaluations.
  • Simplified the match &existing branch since initial and top-up deposits are both validated upfront.
  • Updated docstrings on Error::BelowMinimumResolutionBond and TholosV2::register.
• Test Suite Updates (contracts/tholos-v2/src/test.rs):
  • Updated test_register_top_up_aggregates and test_register_top_up_with_different_commitment_fails to use valid top-up amounts (>= DEFAULT_BOND).
  • Updated test_strict_majority_boundary_requires_more_than_half to register with 101 (>= DEFAULT_BOND 100) to test odd eligible totals without relying on sub-minimum top-ups.
  • Added test_register_top_up_below_minimum_fails asserting top-ups below min_resolution_bond fail with BelowMinimumResolutionBond.
  • Added test_register_dust_top_up_cannot_extend_deadline asserting dust top-ups fail and cannot extend the anti-snipe deadline.
• Documentation (docs/src/CONTRACT_V2.md):
  • Updated the error table description for BelowMinimumResolutionBond.
  • Updated the register function specification to state that all deposits must meet policy.min_resolution_bond.

Verification

• cargo fmt --check passes.
• cargo clippy --workspace --all-targets --locked -- -D warnings passes with 0 warnings.
• cargo test --workspace --locked passes (all 178 unit and proptest tests across all workspace crates).
• cargo build --workspace --lib --target wasm32v1-none --release --locked compiles cleanly.

Payout Routing

• EVM (Base/Arbitrum/Polygon/ETH): 0xF46C9F6d70C50BF81ef3588AB523a90a594a2F89
• Stellar: GCL6OXAMLD75BMTINA6EMRUDWK5THQUSHMYNLSNBCJAPZJHNYJTUNIBC

[collinsezedike]

@s6pa1rta3n-lab Closing. #155 has no assignee. Comment on the issue and wait to be assigned before opening a PR.