fix: wire config freeze gating into set_config

[aliyuHabibu]

• Add ConfigFrozen=16 error variant (InvalidInput renumbered to 17)
• Add require_not_frozen() check in set_config()
• Expose freeze_config/unfreeze_config as admin-gated methods
• Expose is_config_frozen() public query
• Add cfg_frz/cfg_unfrz events with event_schema docs
• Update get_failure_schema with ConfigFrozen and InvalidInput
• Add freeze feature to contract metadata
• Rewrite config_freeze.rs tests (was dead code)
• Add freeze integration tests (lifecycle, auth, events)
• Fix test_pause_rejects_long_reason expected error code

Description

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Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Related Issues

Fixes #(issue number) or relates to #(issue number)

Changes Made

Testing

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• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my own code
• I have commented complex logic
• I have updated relevant documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• My changes do not introduce new warnings

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Closes #3

[Icahbod]

LGTM