Consolidate duplicate functions, fix fill_intent CEI, add struct fields, implement validate_proof - #436

Summary

Four high-priority fixes to the Vortex Protocol's settlement contract, resolving duplicate function definitions, correcting CEI-order violations, adding missing struct fields for merged features, and replacing a no-op proof-validation stub.

Issue #343: Collapse duplicate batch_fill_intent, batch_cancel_intent, get_pending_admin

Removed duplicate function definitions. The duplicates differed only in authorization strategy — one pair called require_auth() per-item (which Soroban forbids), while the other called it once per batch (correct). Consolidated to the CEI-correct single versions:

• batch_fill_intent(): Authorizes solver once at entry, then calls fill_intent_inner() for each fill
• batch_cancel_intent(): Authorizes user once, checks cooldown once, stamps cooldown once, atomically processes all cancels
• get_pending_admin(): Single read-only accessor

Deleted the incorrect duplicates. Added a guard test that parses the exported contract spec and asserts no duplicate function names exist.

Issue #344: Fix fill_intent transferring output twice with undefined fee

Removed the premature DST token transfer that violated CEI ordering (line 2252, before state writes). Removed the incorrect fee calculation using undefined protocol_fee_bps variable (line 2255). Now the function follows strict CEI:

1. Proof validation (if required)
2. All state writes: intent state, solver record, volume/fee accounting
3. Single external call: transfer user output + fee splits

The fee is computed once via get_tiered_fee_bps() with checked arithmetic, honoring volume discounts (#192), and split with referrer when applicable.

Issue #345: Add missing IntentRecord and ProtocolConfig fields

Added four fields required by merged feature branches:

• IntentRecord.referrer: Option<Address> — referral fee-share recipient ([High] Implement an optional on-chain referral fee-share for submit_intent #281)
• IntentRecord.slash_cycles: u32 — slash count toward forced deregistration ([High] Add a cap on repeated Open → Accepted → Slashed cycles per intent #241)
• ProtocolConfig.referral_share_bps: i128 — fraction of fees (0–10,000 bps) sent to referrer
• ProtocolConfig.max_slash_cycles: u32 — solver deregistration threshold

These fields were referenced in fee-split and slash-rate code but did not exist, causing compilation failures.

Issue #346: Replace no-op validate_proof stub

Deleted the second validate_proof definition that did nothing ("In production, this would..."). The remaining implementation now actually verifies:

• Fetches ProofRegistryClient::get_fresh_proof for the intent
• Validates proof.src_chain_id == src_chain_to_wormhole_id(intent.src_chain)
• Validates proof.src_amount >= intent.src_amount
• Maps each failure to the correct error code

Proof-gated fills (require_proof=true) now actually verify the proof instead of silently returning success.

Test Plan

• Verify no duplicate batch_fill_intent, batch_cancel_intent, get_pending_admin in exported spec
• Unit test: single fill matches the CEI output (no double transfer)
• Unit test: fill_intent_inner with referrer and without (fee split correct)
• Unit test: validate_proof rejects mismatched src_chain, insufficient src_amount
• Integration test: hostile-token reentrancy from transfer() is rejected post-CEI state commit
  closes [High] Collapse the duplicated batch_fill_intent, batch_cancel_intent, and get_pending_admin definitions #343
  closes [High] Add the missing IntentRecord and ProtocolConfig fields (referrer, slash_cycles, referral_share_bps, max_slash_cycles) #345
  closes [High] Fix fill_intent transferring the user's output twice and computing the fee from an undefined variable #344
  closes [High] Replace the no-op validate_proof stub so require_proof = true actually verifies the source deposit #346