fix(integrations): declare PiIntegration multi_install_safe (#3652)

* fix(integrations): declare PiIntegration multi_install_safe

PiIntegration writes only to its isolated, static root .pi/prompts,
disjoint from every other integration, yet never declared
multi_install_safe — so it inherited the IntegrationBase default False,
leaving `specify integration status` in a permanent unsafe-multi-install
ERROR state when pi is co-installed alongside another agent.

Add `multi_install_safe = True`, mirroring the isolated MarkdownIntegration
cohort (qwen, shai, qodercli) and the kiro-cli #3471 fix. The parametrized
registry isolation contracts auto-include pi and pass.

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

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

* 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>

---------

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

docs/reference/integrations.md

@@ -276,6 +276,7 @@ The currently declared multi-install safe integrations are:
 | `kilocode` | `.kilocode/workflows` |
 | `kiro-cli` | `.kiro/prompts` |
 | `omp` | `.omp/commands` |
+| `pi` | `.pi/prompts` |
 | `qodercli` | `.qoder/commands` |
 | `qwen` | `.qwen/commands` |
 | `shai` | `.shai/commands` |