docs: close plan 007 and open 008 on the last open audit

All six phases of 007 shipped. The plan moves to completed/ with a recap
rather than a rewrite: its seven "where the plan was wrong" lists are
seventy-nine entries and about a third of them are the audit being wrong,
which is the material 008 is planned against.

008 is a11y.md, the only audit with open items and the least verified
material in the repo. A grep pass closes at least five findings the
coverage map still shows open, including a11y.7, which the map assigns to
phase 6 and which phase 1 fixed. The triage in the plan is recorded as
hypotheses for that reason.

CLAUDE.md

@@ -147,7 +147,7 @@ tree; `make bindings` regenerates it for real.
 `config.toml` and DB rows — the same discipline `sql/schemas/` gets,
 for the same reason.
 
-See `.planning/plans/active/005-agent-development-harness.md`.
+See `.planning/plans/completed/005-agent-development-harness.md`.
 
 ## Architecture