rename docs/ to harness/, and reserve docs/ for the reader

docs/content-model.md opens with "Engine specification". It is also where the
rule lives that a leading underscore makes a file unaddressable — and the human
who owns this site did not know that rule, because nothing in this repository is
addressed to an author. Twelve documents named docs/ while being exclusively
about building the parser is a signpost pointing at the wrong room.

Naming the directory for its audience makes the gap visible instead of hiding it.
docs/ is now reserved and deliberately absent: an empty docs/ is an honest
statement that end-user documentation does not exist, where docs/ full of parser
specs was a claim that it did.

HARNESS.md stays at the root. Root holds the three entry points — README.md for a
human, CLAUDE.md for an agent, HARNESS.md for whoever maintains the machine — and
harness/README.md is the map of the directory, so moving the guide inside would
have collided with it for nothing.

Mechanical and wide: 100 path references across 24 files. Every verify.sh gate
that names a doc by path, the directory lists the dangling-path and ADR-number
gates scan, surface.sh's output target, the Makefile, CLAUDE.md's read order, the
skill, four commands, and two Go package comments. A first pass with a shell loop
silently edited only four files and the rest still said docs/; the fix was to
write the file list out and check the remaining count was zero rather than trust
the loop's exit status.

No rule, threshold, gate or obligation moved — this is a rename, and the gates
demonstrated it twice: they stayed green on the new paths, and the ADR-number gate
caught ADR-0082 before the entry existed.

Deferred, both on the human's call: the end-user documentation site itself, which
wants its own decision about where it lives and whether its claims are gated; and
moving examples/ under docs/, since demo-site is a live site root that verify.sh,
the coverage test and make demo all point at, and moving it would couple a rename
to a design nobody has made.

31 files, +146/-106.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

ideas/specs-as-secondary-artifacts.md

@@ -22,7 +22,7 @@ implemented — flowing upward into the harness where it touches anything the ha
 - Tests are mandatory for `cmd/` and `internal/` changes but nothing ties a test to the rule it verifies.
   `content-model.md` says a bundle key excludes language, and that a bundle supplying both `about.md`
   and `about.en.md` is rejected — nothing checks a test exists for either.
-- One fact, one place is enforced throughout (`docs/README.md` authority table). Specs must not become a
+- One fact, one place is enforced throughout (`harness/README.md` authority table). Specs must not become a
   fourth copy of decisions.
 
 ## The non-overlapping slot