fix: retarget scaffold runtime to solverforge 0.8.8

[blackopsrepl]

Motivation

• The CLI embeds and documents the scaffold runtime target and generated dependency versions, so updating solverforge on crates.io to 0.8.8 requires synchronizing those references in the CLI and its tests.

Description

• Updated scaffold runtime constants and long --version text from 0.8.5 to 0.8.8 in src/scaffold_target.rs.
• Updated the solverforge new generated dependency spec to solverforge = { version = "0.8.8", ... } in src/commands/new.rs.
• Updated scaffold contract tests to assert the 0.8.8 runtime target and generated Cargo.toml content in tests/scaffold_test.rs.
• Aligned repo documentation guidance to reference solverforge 0.8.8 in README.md and AGENTS.md.

Testing

• Ran cargo test for the scaffold suite including test_version_output_distinguishes_cli_from_runtime_target and test_new_readme_records_cli_and_runtime_versions_separately, and the tests passed.
• Ran cargo fmt --all -- --check and it completed successfully.

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Codex Task