Make the sample prompt work in any directory

[sudoHG]

Refs #127

Problem

The sample prompt shown after a client connects asked the agent to run ./deploy.sh --env staging. That script exists only in some projects, so the first try after connecting usually stops with "no deploy.sh here" (seen during the v0.2.0 acceptance with Codex).

Change

• The sample prompt now asks the agent to run a command that checks the credential's variables are set, without printing their values. It works in any directory and with any credential, still goes through approval, and the agent sees only the command's output.
• English and Simplified Chinese strings replaced; the unused sampleCommand constant removed.
• README step 3 (both languages) uses the same prompt and explains that real commands such as ./deploy.sh are asked for the same way.

Checks

• swift build: passed.
• swift test --filter 'AgentAccessPresentationTests|ScreenPresentationTests': 15 passed, 0 failed.
• python3 scripts/check_hygiene.py, python3 scripts/check_module_deps.py, git diff --check: passed.
• Full suite and desktop flows: this PR's CI.