feat(pi): Add Pi coding agent integration

[Doctacon]

Summary

Adds first-class RTK integration for the Pi coding agent via a TypeScript extension.

The Pi extension listens for Pi bash tool calls, delegates rewrite decisions to rtk rewrite, and mutates the bash command in place when RTK has a supported rewrite. This keeps Pi integration thin and reuses the existing RTK rewrite registry.

What changed

• Added hooks/pi/rtk.ts, a fail-open Pi extension for bash tool calls.
• Added rtk init --agent pi install/uninstall support.
• Installs to:
  • ~/.pi/agent/extensions/rtk.ts
  • or $PI_CODING_AGENT_DIR/extensions/rtk.ts when configured.
• Added tests for:
  • --agent pi CLI parsing
  • Pi config path resolution
  • extension install/update behavior
  • dry-run behavior
  • uninstall dispatch routing
• Updated docs:
  • README.md
  • docs/guide/getting-started/supported-agents.md
  • hooks/README.md
  • src/hooks/README.md
  • hooks/pi/README.md

Design notes

• The extension only targets Pi’s bash tool calls.
• All rewrite decisions stay in rtk rewrite.
• The extension fails open:
  • missing rtk
  • rewrite timeout/error
  • unsupported command
  • unexpected extension/runtime error
• This does not change RTK filter behavior or rewrite registry semantics.

Test plan

cargo fmt --all --check
cargo clippy --all-targets
cargo test --all

Also smoke-tested install behavior with an isolated Pi config dir:

TMP_PI_DIR=$(mktemp -d)
PI_CODING_AGENT_DIR="$TMP_PI_DIR" cargo run --quiet -- init --agent pi
cmp -s hooks/pi/rtk.ts "$TMP_PI_DIR/extensions/rtk.ts"

And current-user install:

cargo run --quiet -- init --agent pi
cmp -s hooks/pi/rtk.ts ~/.pi/agent/extensions/rtk.ts

Notes for reviewers

Pi must be restarted or /reload must be run after installation for the extension to become active.

This PR targets develop.

[CLAassistant]

All committers have signed the CLA.

[gitbluf]

Have you checked #1741 ?

[Doctacon]

Have you checked #1741 ?

I hadn't! Thank you for the heads up @gitbluf

[aeppling]

Thanks @Doctacon for participating to PI integration, we've merged #1741 and will be available in RTK 0.42