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.

install.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 # install.sh — install 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):
 #   - pi-env.zsh       : shell loader sourcing ~/.config/pi/.env so AWS_PROFILE
 #                        and AWS_REGION are in every shell that launches pi.
 #   - keybindings.json : mosh/tmux-friendly newline bindings
@@ -98,7 +98,7 @@ link_if_into_repo() {
 require_pi_installed() {
     if [[ ! -d "$PI_AGENT_DIR" ]]; then
         err "pi not detected at $PI_AGENT_DIR"
-        printf '    Install pi first: https://github.com/mariozechner/pi-coding-agent\n'
+        printf '    Install pi first: https://github.com/earendil-works/pi\n'
         printf '    Re-run this installer after `pi` has been started at least once\n'
         printf '    (first run creates ~/.pi/agent/).\n'
         exit 4