NO-SHELL: shrink scripts/tri to 14-line exec shim

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Goal

Move all routing, gen_dir_tree, and pre-flight checks into t27c (Rust). scripts/tri is a pure exec forwarder with --repo-root.

Law

NO-PYTHON / NO-SHELL — tooling lives in t27c.

Status

Core implementation is already on master (14-line scripts/tri, clap routing, NOW gate in run_rest, directory batch on gen/gen-c/gen-verilog, skill-seal, brain stub).

This issue tracks closure and doc alignment. PR will update TRINITY-BRAIN TZ examples (skill-seal, exec shim note).

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PR opened: #161 — doc alignment for exec-only tri. Rust/shim work is already on master.