feat(onchain): add standardized ContractVersion struct and version() introspection to core contracts

[harryjupiter148]

Summary

This PR adds standardized on-chain version introspection to all core Lumenpulse Soroban contracts:

• Shared version crate: Created contracts/version introducing the canonical ContractVersion struct (contract, major, minor, patch, min_interface) carrying #[contracttype].
• Core contract methods: Implemented pub fn version(env: Env) -> ContractVersion on 7 core contracts (lumen_token, project_registry, yield_vault, matching_pool, crowdfund_vault, contributor_registry, treasury).
• Zero rent/storage cost: The version query is pure and returns compile-time constants without consuming ledger storage or requiring caller authentication.
• Documentation & Validation: Added apps/onchain/VERSION_INTROSPECTION.md explaining schema, compatibility checking logic (min_interface), and release validation patterns. Verified with dedicated unit tests across all 7 contracts.

Linked Issue

Closes #1046

Type of Change

• feat
• fix
• docs
• refactor
• test
• chore

Validation

• Lint passed for affected area(s)
• Tests passed for affected area(s)
• Manual verification completed (if applicable)

Documentation

• Documentation updated (or N/A with explanation)
• Screenshots/videos attached for UI changes

Checklist

• Branch name uses feat/, fix/, or docs/
• Commit messages follow Conventional Commits
• PR scope matches linked issue acceptance criteria

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[Cedarich]

Kindly fix failing CI

[Cedarich]

Kindly resolve conflicts

[Cedarich]

@harryjupiter148