Rename github URL refs to earendil-works/pi

Pi moved to its new home at earendil-works on 2026-05-07
(https://pi.dev/news/2026/5/7/pi-has-a-new-home).

URL substitution:
  https://github.com/mariozechner/pi-coding-agent
  -> https://github.com/earendil-works/pi

(coding-agent now lives at packages/coding-agent inside the new
monorepo root, but linking to the root is the canonical reference
per the announcement post).

Brew install references (`brew install pi-coding-agent`) left as-is:
the homebrew formula still works at 0.73.1 and a tap update is
tracked upstream at earendil-works/pi#2755.

README.md

@@ -1,6 +1,6 @@
 # pi-toolkit
 
-Harness-side bring-up for the [pi coding-agent](https://github.com/mariozechner/pi-coding-agent).
+Harness-side bring-up for the [pi coding-agent](https://github.com/earendil-works/pi).
 
 **What's here:**
 - `pi-env.zsh` — loads `~/.config/pi/.env` into every shell so pi's Bedrock provider has `AWS_PROFILE` / `AWS_REGION` available.
@@ -36,7 +36,7 @@ Requires pi to be installed first (`~/.pi/agent/` must exist). Install via:
 
 ```bash
 brew install pi-coding-agent              # macOS
-# or see https://github.com/mariozechner/pi-coding-agent for Linux
+# or see https://github.com/earendil-works/pi for Linux
 pi --help                                 # first run creates ~/.pi/agent/
 ```
 
@@ -89,7 +89,7 @@ If you don't use a dotfiles repo, create the file manually after step 3 (install
 
 ```bash
 brew install pi-coding-agent              # macOS
-# or see https://github.com/mariozechner/pi-coding-agent for Linux
+# or see https://github.com/earendil-works/pi for Linux
 pi --help                                 # creates ~/.pi/agent/
 ```