feat: define project configuration schema

[dDevAhmed]

Summary

Implements CLI-034 with a versioned, project-root StellarForge configuration contract and safe deployment integration.

Included

• adds stellarforge.config.json MVP schema
• requires version: 1
• supports explicit network and named Stellar CLI identity
• records configuration architecture in ADR-0005
• documents loading rules and precedence
• loads only a fixed project-root JSON file
• rejects symbolic links, non-files, oversized config, malformed JSON, unknown fields, secret-bearing fields, raw Stellar StrKeys, and unsafe identity values
• resolves CLI options above project configuration
• keeps missing values missing instead of silently defaulting a network
• integrates resolved configuration with stellarforge deploy
• keeps deploy command Testnet-only after configuration resolution
• adds unit and command-level coverage for validation, missing configuration, precedence, redaction, and deployment consumption

Precedence

CLI option > stellarforge.config.json > missing

Environment-variable precedence is intentionally outside the MVP.

Security

• no executable JS/TS configuration
• no implicit Mainnet/default network
• no raw signing material in project configuration
• secret-like fields are rejected without echoing values
• Stellar CLI remains the signing-material boundary
• deployment still enforces Testnet independently of configuration

Closes #37

[dDevAhmed]

Closing as duplicate/superseded: CLI-034 has already been merged to main via #80, and #81 contains newer documentation changes on top of it. Merging this branch would reintroduce stale history and duplicate the completed configuration work.