fix(server): sanitize runtime exception responses

[knqiufan]

Summary

• Sanitize runtime dependency probe failures before they reach /api/v1/system/status, and keep raw probe exceptions in server logs only.
• Replace request-path service APIError messages and batch item errors that previously embedded str(e) with generic public messages.
• Add regression coverage for synthetic DSN/secret/path exposure in dependency checks, status dependencies, service-layer errors, and batch response data.

Stack note

• This branch is stacked on fix(server): sanitize startup errors in API responses #1136 because Runtime dependency check and request-path errors still expose raw exceptions in API responses #1137 reuses the safe startup-error helpers added there.
• The Runtime dependency check and request-path errors still expose raw exceptions in API responses #1137-specific commit is a37bb5d (fix(server): sanitize runtime exception responses). After fix(server): sanitize startup errors in API responses #1136 merges, this PR diff should collapse to the Runtime dependency check and request-path errors still expose raw exceptions in API responses #1137 changes only.

Test plan

• python -m pytest tests/unit/server/test_health_check.py tests/unit/server/test_system_health.py
• python -m pytest tests/unit/server
• git diff --check
• python -m pytest tests/unit was attempted locally; it still fails on unrelated local environment/tool assumptions, including API/model environment overrides, missing ModelScope cache, Windows script/tool availability, and an existing sqlite FTS setup error.

Fixes #1137

[wayyoungboy]

LGTM