pi: add agent config, themes, subagents, and extensions

.pi/agent/extensions/plan-mode/README.md

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+# Plan mode extension
+
+Claude Code-style plan mode for pi.
+
+## Features
+
+- `/plan` toggles read-only planning mode
+- `Ctrl+Alt+P` toggles plan mode on/off
+- `/plan execute` runs the last approved plan in the current session with full tools restored
+- `/plan execute fresh` starts a fresh session and carries the approved plan into it for execution
+- extracts numbered steps from a `Plan:` section
+- tracks progress with `[DONE:n]` markers during execution
+- restores your previous active tool set after plan mode ends
+- keeps `subagent` available in plan mode when you intentionally want to use helper agents during planning
+
+## Commands
+
+- `/plan`
+- `/plan on`
+- `/plan off`
+- `/plan execute`
+- `/plan execute fresh`
+- `/plan status`
+- `/plan clear`
+
+## Shortcut
+
+- `Ctrl+Alt+P` — toggle plan mode
+
+## Behavior
+
+When plan mode is enabled, pi switches to read-only exploration and asks the model to produce a numbered `Plan:` section.
+
+After planning finishes, the extension shows a chooser so you can:
+- execute now
+- execute in a fresh session
+- send custom feedback / continue discussion
+- stay in plan mode
+
+When you execute the plan in the current session, the extension restores your previous tools and asks the model to complete the steps while emitting `[DONE:n]` markers.
+
+If you use `/plan execute fresh`, the extension creates a new session, carries over the approved plan and planner notes, restores the full tool set there, and starts execution in that fresh context.