feat(pi): add Pi (pi.dev) as a sixth CLI run mode (#206)

SessionMode gains 'pi', a first-class backend alongside Claude Code,
OpenCode, Codex, Gemini and Antigravity: its own PTY, tmux session, rose
tab identity, welcome button, run-mode entry, cron agentType, Docker and
remote-SSH command defaults, and clone-repo Brain option.

Pi is a different shape of CLI from the other four, and three decisions
follow from that:

- It has NO permission prompts and no sandbox, so there is no
  --dangerously-skip-permissions analog and none was invented. The
  privilege-shaped knob is the tri-state approveProjectTrust, which makes
  pi load and EXECUTE repo-local .pi/extensions TypeScript and install
  missing project packages. clampExternalCliBypassForOwner() therefore
  puts pi in the MATERIALIZE branch: a non-granted multi-user owner gets
  --no-approve even when no config was sent, because pi's own default is
  a prompt the session user could answer themselves. That helper had zero
  test coverage; it now has coverage for all four CLIs.
- Only the PI_ prefix joins the env allowlist. Pi's ~34 provider key vars
  share no prefix and ALLOWED_ENV_PREFIXES is one global list with no mode
  context, so admitting them would widen the allowlist for every mode at
  once. Auth goes through pi's /login or the server's own environment.
  --api-key is deliberately never wired: it would put a provider secret on
  the spawn command line.
- pi stays OUT of isAltScreenStripMode(). Its default TUI renders into the
  main screen with terminal-owned scrollback, and its 0.84.0 fullscreen
  mode is runtime-switchable via /settings; that flip was measured to put
  the pane into the alt screen, which the strip would have corrupted.

pi-cli-resolver.ts additionally sanity-probes `pi --version` and requires
semver-shaped output, because `pi` is a short generic name a stray binary
can shadow; GET /api/pi/status surfaces path and version so a
misresolution is diagnosable rather than presenting as a broken mode.

Docker installs pi in its own --ignore-scripts step so that flag cannot
affect the other four CLIs, and seeds its credentials per-file rather than
whole-dir (~/.pi/agent also holds sessions, extensions and package trees).

Verified end to end against pi 0.84.1 on an isolated instance: resolver
search-dir fallback, flag construction, piConfig persistence across a full
server restart, the trust prompt and its --no-approve suppression, the
rose Run button on the default daylight-blue skin (the nested skin block
eats per-mode gradients unless the rule lives inside it), and the buffer
local-echo policy, which pi tolerates where codex did not.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/docker-cases.md

@@ -2,7 +2,7 @@
 
 Run a case inside an **isolated Docker container** instead of directly on the host. Any number of Codeman sessions can share one container (it is scoped to the case, not the session), so a whole project lives in a sandbox with its own network, resource caps, and filesystem, and you can **export the container to move it to another machine**.
 
-Docker mode is a **location overlay on cases**, the direct analog of [remote SSH cases](./remote-hosts.md): where a remote case runs a local tmux pane doing `ssh host` into a durable remote tmux server, a docker case runs a local tmux pane doing `docker exec -it` into a durable **in-container** tmux server. It is not a separate `SessionMode`, so `claude` / `shell` / `opencode` / `codex` / `gemini` / `antigravity` all work inside the container.
+Docker mode is a **location overlay on cases**, the direct analog of [remote SSH cases](./remote-hosts.md): where a remote case runs a local tmux pane doing `ssh host` into a durable remote tmux server, a docker case runs a local tmux pane doing `docker exec -it` into a durable **in-container** tmux server. It is not a separate `SessionMode`, so `claude` / `shell` / `opencode` / `codex` / `gemini` / `antigravity` / `pi` all work inside the container.
 
 ## One-time setup: build the base image
 
@@ -25,10 +25,12 @@ A zero exit code only proves the layers ran, not that the toolchain works. Verif
 
 ```bash
 docker run --rm codeman/agent:base bash -lc \
-  'for c in claude codex gemini opencode agy; do printf "%-9s " $c; $c --version 2>&1 | head -1; done'
+  'for c in claude codex gemini opencode agy pi; do printf "%-9s " $c; $c --version 2>&1 | head -1; done'
 ```
 
-Antigravity (`agy`) is the one CLI not installed from npm (Google ships a standalone binary), so it has its own Dockerfile step and adds roughly 190MB; a full image lands near 1.6GB.
+Antigravity (`agy`) is the one CLI not installed from npm (Google ships a standalone binary), so it has its own Dockerfile step and adds roughly 190MB; a full image lands near 1.6GB. Pi also gets its own step, because upstream documents installing it with `--ignore-scripts` and that flag must not silently change how the other four npm CLIs install.
+
+Pi's credentials are seeded per-FILE rather than as a whole directory (`auth.json`, `settings.json`, `trust.json`, `models.json`, `models-store.json` out of `~/.pi/agent`), because that directory also holds `sessions/`, `extensions/`, `skills/` and the installed package trees — gigabytes on an active host. Consequence: in-container pi sessions are invisible host-side, so `pi -c` inside a Docker case only sees that container's own history. See [`pi-integration.md`](./pi-integration.md).
 
 ## Quickest path: one-click "Run in Docker"