docs(onboarding): make deploy/compose the primary onboarding path (#109)

[waterbro-8]

Requirement and scope

Re-lands the #109 onboarding repositioning on an organization branch. Previous candidate #148 was closed because it was a fork head without CI, not because the content was rejected.

Refs #109 R1: REQ-001–003 / AC-001–003.

Changes

• README 快速开始 leads with deploy/compose (generate-env → compose up --wait → curl /healthz → register at http://localhost:8080 → CLI). Commands match docs/DEPLOYMENT.md.
• Bare-metal ./scripts/dev_up.sh is a development-only subsection.
• docs/RUN_LOCAL.md is labeled development-only and adds macOS / Ubuntu/Debian / WSL2 equivalents for PostgreSQL+pgvector, MinIO, Ollama, and the TESTING.md toolchain pins.
• [Unreleased] changelog entry.
• No compose topology or service changes.

AC-003 (first-run messaging) is already satisfied on main by mem doctor / no-credential hints naming deploy/compose (#112). This PR does not retouch that code.

Validation ledger

ID	Criterion	Command	Status
V1	Docs fixture: README leads with compose; bare-metal demoted	read README / RUN_LOCAL	PASS (source)
V2	Compose command sequence matches DEPLOYMENT.md	compare generate-env / compose.yaml / curl :8080/healthz	PASS (source)
V3	Closed-loop runbook on a clean host (up → register → folder create)	deploy/compose on a clean machine	NOT VERIFIED in this environment — no Docker daemon here
V4	Doctor first-run names compose	existing cmds_doctor_test.go on main	already on main; not re-run
V5	git diff --check	local	PASS

No merge, release, or issue closure is claimed. Independent review still required.

[waterbro-8]

CI is green. I cannot approve or merge: I am the author. Needs @PeterGuy326 or @Bindy-lbb.

[waterbro-8]

请评审合入（作者是我，不能自批）。

README 主路径改为 deploy/compose，裸机降为开发说明，并补了 Ubuntu/WSL2 对照。CI 已绿。

需要 @PeterGuy326 或 @Bindy-lbb 批准。

[PeterGuy326]

Independently reviewed current head 0ca8b53 against base 1b27aac. The documentation diff is scoped to onboarding guidance and platform-equivalent local development instructions; git diff --check passes and the required CI checks are green. The unavailable clean-host Docker run is explicitly disclosed in the validation ledger. No blocking finding remains; approving as a non-author CODEOWNER.