NER-380: Split CLI facade args and core handlers

[freezscholte]

Summary

• move CLI clap definitions into crates/forge-cli/src/args.rs
• move remaining non-sync/export CLI handlers and helpers into crates/forge-cli/src/commands/core.rs
• reduce crates/forge-cli/src/main.rs to dispatch/output facade scope and update ADR-0001

Verification

• rtk cargo fmt --all --check
• scripts/check-rust-line-count.sh
• rtk cargo test --workspace (603 tests / 61 suites)
• rtk cargo clippy --workspace --all-targets -- -D warnings
• rtk bash scripts/ci.sh (PASS=95 FAIL=0)

Linear: NER-380

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