docs(integrations): list pi in the multi-install-safe reference table

Declaring PiIntegration multi_install_safe means the reference table in
docs/reference/integrations.md (which states it lists all currently
declared multi-install-safe integrations) should include it. Add the
alphabetized pi row with its .pi/prompts isolation path.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: jawwad-ali

docs/reference/integrations.md

@@ -275,6 +275,7 @@ The currently declared multi-install safe integrations are:
 | `junie` | `.junie/commands` |
 | `kilocode` | `.kilocode/workflows` |
 | `kiro-cli` | `.kiro/prompts` |
+| `pi` | `.pi/prompts` |
 | `qodercli` | `.qoder/commands` |
 | `qwen` | `.qwen/commands` |
 | `shai` | `.shai/commands` |