docs: Add complete SIP-010 fungible token implementation example

[Earnwithalee7890]

Description

Adds a comprehensive SIP-010 fungible token example to help developers implement the standard correctly.

Changes

• ✅ Complete SIP-010 implementation with all required trait functions
• ✅ Practical usage examples (minting, transferring, checking balances)
• ✅ Deployment and testing instructions
• ✅ Best practices and customization guide
• ✅ Security considerations (access control, validation)

Why This Helps

Many developers ask for complete, working SIP-010 examples. This provides:

• Production-ready reference implementation
• Clear explanation of each function
• Testing and deployment guidance
• Common customization patterns

Testing

• Contract code compiles with Clarinet
• All SIP-010 trait functions correctly implemented
• Examples are clear and runnable
• Documentation is comprehensive

Related

• Addresses community requests for token implementation examples
• Complements existing SIP-010 trait documentation
• Helps onboard new Clarity developers

[CLAassistant]

All committers have signed the CLA.