[jdjioe5-cpu]

Summary

Resolves #2343.

As discussed by maintainers (@leighmcculloch, @mootz12), the Stellar CLI preserves standard industry precedence:
CLI Arguments/Flags > Environment Variables > CLI Config Defaults (\stellar network/keys/fees use) > Built-in Defaults

This PR explicitly documents the precedence rules across user-facing documentation, command descriptions, and developer skill guidelines, and adds unit testing:

1. README.md: Adds a dedicated \Configuration and Precedence\ section explaining the 4-tier resolution hierarchy and references \stellar env.
2. Commands Help: Documents precedence order in the doc comments for both \Config\ and \Env\ subcommands in \cmd/soroban-cli/src/commands/mod.rs\ and \commands/cfg/mod.rs.
3. SKILL.md: Adds precedence callout notes in the Networks and Identities guides to avoid silent override confusion when environment variables are present.
4. Unit Tests: Adds \ est_set_env_value_from_config_precedence\ in \cli.rs\ verifying that explicit environment variables strictly take precedence over config defaults.

Verification

• \cargo test --package soroban-cli --lib cli::tests: All tests pass.
• Verified doc render and formatting.