fix(applaunchpad): align log field labels

[Kianwillbefine]

What changed

• Use the same display label for log field settings and table headers.
• Keep raw field keys unchanged for data access and filtering.
• Add regression coverage for _time, _msg, and ordinary fields.

Why

The field settings showed raw _time and _msg keys while the table headers showed time and msg, so the descriptions for the same fields did not match.

Verification

• vitest run --config vitest.config.ts: 19 files, 103 tests passed
• tsc --noEmit -p tsconfig.json: passed
• next lint: passed with pre-existing hook dependency warnings
• prettier --check: passed
• Browser verification: expanded field settings and table headers both show time and msg

Fixes labring-sigs/sealos-issues#356