fix(cli)!: remove dead flags and empty stats dimensions

[pablontiv]

Summary

Final Slice C of the issue #66 chain removes the remaining dead CLI surface:

• changes stats JSON to version 2 with the honest total-only contract (version, kind, total);
• removes the unused describe --by-domain and set --create flags;
• removes unsupported += syntax from set help while retaining explicit rejection;
• synchronizes README, stats documentation, CLAUDE guidance, and the Rootline skill.

The residue was re-derived against master and the issue #63 chain branch pablontiv/w5-issue63-field-contract; issue #63 removed none of this surface. This slice intentionally leaves the existing stats filter invocation unchanged so the issue #63 field-contract changes remain isolated.

Verification

Strict TDD recorded RED before production edits, then GREEN. Independent verification passed:

• just check — 0 lint issues;
• just test — all packages passed with race detection;
• just coverage-check — 89.6% total, lowest configured package 86.9%;
• focused contract checks — 6/6 passed;
• native bounded reliability review — approved with no findings.

Chain

PR #131 → PR #133 → this PR. This PR targets pablontiv/w5-issue66-repair-surface. Per #130, stacked PRs with a non-master base currently receive zero GitHub checks; the complete local verification evidence above governs this slice.

Closes #66

[pablontiv]

Orchestrator verification — local CI equivalence at e790bdc

This PR is stacked on pablontiv/w5-issue66-repair-surface, so per #130 GitHub fires no workflow and statusCheckRollup is empty. Every non-push-gated ci.yml job was reproduced locally against head e790bdc in a detached worktree.

ci.yml job	Local equivalent	Result
ci / Test & Build	just check	0 lint issues, go build ./... clean
ci / Test & Build	just test (go test ./... -race)	14/14 packages ok
ci / Test & Build (coverage 85%)	just coverage-check	TOTAL 89.6%, lowest package cmd/rootline 86.9%
ci / Tidy	go mod tidy + git diff go.mod go.sum	no diff
docs-validate	branch-built binary, rootline validate --all docs/roadmap/	127/127 valid, 0 errors
installer-tests (ubuntu/macos)	sh tests/installers/install-sh-test.sh	passed
installer-tests (windows)	not reproducible on this host	n/a — no installer file in this diff
gitleaks / Secret scanning	gitleaks detect --source .	no leaks, 1025 commits scanned
release, installer-smoke	push-gated (github.event_name == 'push')	never run on a PR

Commit hygiene: exactly one commit, subject identical to the PR title, breaking marker ! present, no AI attribution or Co-Authored-By trailer. Both halves of the .githooks/pre-push cmd/rootline/ gate are satisfied (docs/stats.md + README.md + CLAUDE.md, and .claude/skills/rootline/SKILL.md).

Merge order for the #66 chain: #131 → #133 → #135. Retarget each child to master before merging its parent — gh pr merge --delete-branch on a stacked base closes the child and GitHub refuses to reopen it. When squashing, keep the fix(cli)!: title so the breaking change is not released as a plain patch.