[docs] Align contributor setup and hook instructions with current tooling #2148

Problem

On develop 0d65f2ad, the contributor guides differ from the commands a new contributor actually runs:

• The quick start installs Python dependencies but omits dashboard/npm ci, even though make all immediately invokes frontend Prettier.
• The documented Node 18 prerequisite does not satisfy current locked dependencies, including an ESLint visitor-keys requirement supporting Node 22 from 22.13.
• The guides describe the hook as make all; .githooks/pre-commit actually invokes make precommit (testmon-selected tests), then the dashboard build.
• make check-all runs full-stack lint/type checks and backend tests, but not Vitest; the frontend test command is not shown in the setup flow.
• The root README-only hook exception is not described.

Proposed solution

Calibrate the English/Chinese quick start and AGENTS hook guidance against the actual Makefile and hook: install npm dependencies, choose develop, document a compatible Node version, show the frontend test command, and distinguish the local hook from the full backend ship gate.

No hook or application behavior change is proposed.

Related work / duplicate check

• docs(contributing): distinguish the local hook from the full test gate #1555 covered part of the hook wording, but is closed without merging.
• docs(makefile): fix make help drift on the pre-commit gate #1584 covers Makefile help text; this request does not change that file.
• docs(agents): repair module paths that no longer exist #908 covers stale module paths; those edits are excluded here.

Verification

Cross-checked Makefile targets, actual hook commands and both language sections. Full backend ship gate on the same source base passed: 4969 passed, 34 skipped.