Finish wiring draft_reason on main

This page is a capture in the inbox bucket of the product backlog — a pre-sprint idea, not yet pulled into a sprint as a story.

1. What

Main carries the draft_reason entity (commit 5ff1c72221) without its wiring. Six local checks fail on it:

handler-permissions: trading::draft_reasons:read, :write and :delete are checked but never seeded.
sql-reachability and er-diagram: trading_draft_reasons_drop.sql and trading_draft_reasons_notify_trigger_drop.sql are in no aggregator.
tangle-shell and recipe-inventories: its shell scripts and the shell recipe inventory are not committed.
codegen-tests: the trading shell aggregator renders draft_reason_commands, which test_the_aggregator_lists_every_opted_in_trading_unit does not expect. It fails with main's model, so the reflect-cpp branch did not cause it.

Its C++ files were also missing from the CMake component lists. PR #4278 fixes that part.

Every branch's local gate fails on these checks until main finishes the entity.