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.

AGENTS.md

@@ -2,7 +2,7 @@
 
 ## What this is
 
-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).
 Installs three pi-generic config artifacts into the right places and
 runs a couple of non-halting probes. Does not depend on MemPalace.
 
@@ -150,7 +150,7 @@ echo "# local edit" >> ~/.oh-my-zsh/custom/pi-env.zsh
 
 - **pi must be installed upstream first.** `~/.pi/agent/` is created by
   pi on first run, not by this installer. Missing → exit 4 with
-  pointer to https://github.com/mariozechner/pi-coding-agent.
+  pointer to https://github.com/earendil-works/pi.
 - **`settings.example.json` is region-specific.** The shipped default
   uses `eu.` Bedrock inference-profile prefixes. Users on us-east need
   to swap to `us.` before first run, or pi will reject the model ID.