fix(safety): O107 credential path realpath / symlink follow-up (#100 O105)

[QiaolongLi1201]

Summary / 摘要

O107 (P3) — follow-up to #100 (O105).

isMossCredentialPath only used path.resolve, so a workspace symlink pointing at .moss/config.json, .moss/devices.json, ~/.moss/*, ~/.config/moss/*, or .apikey-key bypassed the O105 readFileTool.execute → presentToolOutput gate and returned plaintext secrets.

O105 合入后 QA PASS-WITH-CONDITIONS：软链 / realpath 跟进。本 PR 只加严：对 credential 路径做 realpath（及 dangling 时的 readlink），与 protected-paths / canonicalPath 同精神。无 kill-switch，不放宽任何 O105 断言。

Changes / 改动

• src/safety/read-scope.ts: credentialPathFollowCandidates + isMossCredentialPath follows realpath / readlink target
• src/safety/credential-path.ts: isRawApiKeyFile uses the same follow so symlink→.apikey-key still withholds
• test/o107-credential-realpath.spec.mjs: symlink→config/devices redact; ordinary notes symlink plaintext; dangling→config fail-closed; revert-red smoke

Acceptance / 验收

Check	Result
Symlink → .moss/config.json (fake apiKey): execute no plaintext, [REDACTED]; isMossCredentialPath(link) true	pass
Symlink → .moss/devices.json password	pass
Symlink → ordinary notes.txt	plaintext, not credential
Revert-red: lexical-only isMossCredentialPath + basename-only isRawApiKeyFile → 6/8 fail; restore → 8/8 pass	pass
O105 suite + read-scope.spec.mjs	10/10 pass
npm run check	green

Test plan

npm run build
node --test test/o107-credential-realpath.spec.mjs
node --test test/o105-config-credential-read.spec.mjs test/read-scope.spec.mjs
npm run check

Head: d5aec5ca · Base: 9629e423 (#100 merge).

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