[ALL] Complete Quantstamp Audit Remediation - All Findings Resolved

Comprehensive integration of all Quantstamp security audit fixes for trails-contracts.

This PR consolidates all audit findings and recommendations:

Audit Findings Fixed:
- SEQ-1 (High): Unsigned fee parameters + permit validation ✅
- SEQ-2 (Medium): Non-standard ERC-20 token compatibility ✅
- SEQ-3 (Low): Multicall3 allowFailure validation ✅
- SEQ-4 (Low): IMulticall3 interface correctness ✅
- SEQ-5 (Low): Redundant self-approvals removed ✅
- S1: Custom errors over require statements ✅
- S2: Unused helper functions removed ✅
- S3: Code duplication eliminated ✅

Key Security Improvements:
1. TrailsIntentEntrypoint: Fee integrity, token compatibility, permit validation
2. TrailsRouter: Silent failure prevention, gas optimization, code quality

Testing: 148/148 tests passing across all contracts

Audited Commit: ca3916e
Final Commit: f36f3e8

Related PRs: #57 (SEQ-2), #58 (SEQ-3), #59 (S2), #60 (S3), #61 (TrailsRouter), #62 (SEQ-1)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: shunkakinoki