fix(timeout): reject invalid request-timeout flags

[JerryNee]

Summary

• centralize parsing for the global --request-timeout <seconds> flag
• reject explicit invalid values such as abc, 0, 1.5, and 601 with a local VALIDATION_ERROR instead of silently using/rounding/clamping another timeout
• keep env/direct factory timeout resolution behavior unchanged while wiring auth/project/test/usage/setup through the shared flag parser

Repro

Before this change, testsprite project list --dry-run --request-timeout abc exited 0 and used the default timeout. After this change it exits 5 with a machine-readable VALIDATION_ERROR naming request-timeout.

Verification

• npm test -- src/lib/client-factory.test.ts
• npm test -- test/cli.subprocess.test.ts
• npm run lint
• npm run typecheck
• npm test
• npm run build
• node dist/index.js --output json project list --dry-run --request-timeout abc