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

[Yoonkeee]

What happened?

PR #670 made PI_RULES_DISABLED, PI_RULES_MAX_RULE_CHARS, and PI_RULES_MAX_RESULT_CHARS supported public settings and documented them in the coding-agent README, but the Environment Variables section of senpi --help does not list them.

This matters especially for the two character limits because they have no equivalent CLI flag or senpi config field. I can send a focused PR to keep the help output aligned with the released settings.

Steps to reproduce

$ senpi -ne --help | rg 'PI_RULES'
$ echo $?
1

The same empty result occurs without -ne.

Expected behavior

senpi --help lists all three settings with the same semantics and defaults as the README:

• PI_RULES_DISABLED
• PI_RULES_MAX_RULE_CHARS (default: 12000)
• PI_RULES_MAX_RESULT_CHARS (default: 40000)

Version

2026.8.3-3

[Yoonkeee]

AI-assisted disclosure: I used Codex to help inspect the repository conventions and draft this report. I personally reproduced the released CLI behavior and verified the README/runtime mismatch before filing it.