feat(server): add Pi agent provider and re-enable Copilot (#191)

* fix(app): reorder settings sections for better grouping

* feat(app): add setup hint and paseo.sh link on mobile welcome screen

New app store users land on the welcome screen with no context. Show a
brief explanation that the desktop app or server is needed, plus a link
to paseo.sh — only on mobile (iOS/Android), hidden on web/desktop.

* docs(release): add pre-release sanity check and clarify changelog scope

Add a Codex 5.4 review step before cutting releases to catch breaking
changes and backward-compatibility issues (mobile apps lag behind
desktop/daemon updates). Clarify that the changelog always covers the
delta from the previous stable release, not from the last RC.

* feat(server): add Pi agent provider and re-enable Copilot

Add Pi (pi.dev) as a new ACP-based agent provider with bundled pi-acp
adapter. Pi-acp reports thinking levels as ACP modes and bash tool calls
with kind "other", so the Pi provider uses generic ACP extension hooks
to remap these to the correct Paseo concepts:

- sessionResponseTransformer: remaps ACP modes → configOptions[thought_level]
- thinkingOptionWriter: writes thinking via setSessionMode instead of
  set_config_option (which pi-acp doesn't support)
- toolSnapshotTransformer: remaps bash tool kind from "other" to "execute"
- modelTransformer: cleans slash-prefixed model labels

Also re-enables the Copilot provider (disabled since 44da0c67) and
removes the claude-acp provider.

* fix: update lockfile signatures and Nix hash

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

nix/package.nix

@@ -42,7 +42,7 @@ buildNpmPackage rec {
 
   # To update: run `nix build` with lib.fakeHash, copy the `got:` hash.
   # CI auto-updates this when package-lock.json changes (see .github/workflows/).
-  npmDepsHash = "sha256-rbw+tXNKO7lNRNG6cdlaLyLLaEEdMzDD/Ob7/8noeKw=";
+  npmDepsHash = "sha256-pZGDc2JVlxKz6TvuM7ALD2RzXq/ANzvmJiV+bge/SL4=";
 
   # Prevent onnxruntime-node's install script from running during automatic
   # npm rebuild (it tries to download from api.nuget.org, which fails in the sandbox).