fix(coding-agent): list PI_RULES settings in --help

[Yoonkeee]

Summary

• list PI_RULES_DISABLED, PI_RULES_MAX_RULE_CHARS, and PI_RULES_MAX_RESULT_CHARS in the top-level Environment Variables help
• keep accepted values and defaults aligned with the runtime and README added in fix(coding-agent): honor PI_RULES environment settings #670
• add an issue-numbered help regression and the required fork changes.md record

Closes #678

Root cause

printHelp() maintains its Environment Variables section independently. PR #670 added the runtime settings and README rows, but did not update that static help surface. The two character limits have no equivalent CLI flags, so they were otherwise undiscoverable from senpi --help.

RED -> GREEN

• npx vitest --run test/suite/regressions/678-pi-rules-help-env.test.ts
  • RED: 1 failed because PI_RULES_DISABLED was absent from top-level help
  • GREEN: 1 passed after adding the three rows
• adjacent help coverage: 3 files, 82 tests passed

Verification

• npm run check
• npm run build
• no-excuse TypeScript audit: no violations in the two changed TS files
• repository QA self-check: 9/9 passed
• CLI smoke self-test: 8/8 passed
• hands-on review QA: 20/20 scenarios passed, including --help, -h, duplicate detection, exact defaults, and invalid environment values
• five-lane review plus runtime audit: all passed at 30188918f96d033def3eaaf48af4273512a60c42

Built/source CLI observation:

PI_RULES_DISABLED                - Disable built-in rules when set to 1/true/yes/on
PI_RULES_MAX_RULE_CHARS          - Per-rule formatted payload character cap (default: 12000)
PI_RULES_MAX_RESULT_CHARS        - Complete static/dynamic block character cap (default: 40000)

Both normal and -ne help invocations exited 0 with empty stderr.

The full coding-agent suite reached 6745 passing tests with one unrelated timing-sensitive issue #5303 assertion failing under full-suite load; that test file passed 2/2 immediately in isolation. No production behavior in that path is changed here.

Scope

• README is unchanged because fix(coding-agent): honor PI_RULES environment settings #670 already documents the correct contract.
• CHANGELOG.md is intentionally unchanged per repository policy.

---

Summary by cubic

Add the PI_RULES_DISABLED, PI_RULES_MAX_RULE_CHARS, and PI_RULES_MAX_RESULT_CHARS env vars to the top-level --help so users can discover and configure rule behavior. Aligns help with the runtime and README. Fixes #678.

• Bug Fixes
  • Added help entries for the three PI rules env vars with accepted values and defaults.
  • Added a regression test to ensure these settings appear in top-level help.

^{Written for commit 3018891. Summary will update on new commits.}