docs: English-only docs/ + root AGENTS.md (dev conventions + .changes rules)

[btspoony]

Summary

User directive (2026-08-14): docs/ must be English-only or bilingual (decision: English-only, matching README.md + CHANGELOG.md); plus a root AGENTS.md documenting .changes/ fragment rules and development conventions.

Docs translation (3 parallel tracks, L2 worktree isolation)

• docs/configuration.md + docs/verification.md (Track A)
• docs/install.md + docs/release.md + docs/consumer-api.md (Track B)
• Commands/code blocks/YAML/tables/test counts preserved verbatim; only prose translated. CJK residual ≤ 1 per file (the real dsh UI label 插件配置, per README convention).
• QC caught + fixed stale content carried over from the Chinese originals: test counts refreshed to 23 files / 460 tests; legacy chains/chains.default references rewritten to the two-block model (rootChain / roles.list / roles.rules); §2/§4.2 conflict-banner contradiction resolved against source.

Root AGENTS.md (Track C)

• New AGENTS.md (123 lines, English): source priority, repo identity, build/test interface, .changes/unreleased/ fragment rules (one file one category, English-only bullets, zero fragments = publish failure), docs English-only rule, PR-driven release flow (zero secrets), code constraints (mount-only, public-registry peers, EN commits, branch → PR → main), harness SSOT note.

Verification

• QC single-seat (docs-only): Request Changes → fix wave (verification.md) + micro-fix (release.md baseline) → re-review Approve (zero-residual)
• pm-acceptance: no open R#; CJK sweep final: ≤1 per file (UI label only); no code/test/workflow changes in the diff