feat: improve execution mode (Plan/Build/Yolo) visibility, documentation, and UX

[Crempa]

Problem

Execution mode (Plan / Build / Yolo) controls permission flags injected into agent preset commands, but it is poorly discoverable, undocumented, and its interaction with preset configuration is confusing.

Current issues

1. Confusing preset editor behavior: The preset editor displays the raw configured command (e.g. claude --dangerously-skip-permissions), but at launch time the permission flags are silently stripped and replaced based on the current execution mode. A user who sets --dangerously-skip-permissions in their preset and is in Build mode will actually get --permission-mode acceptEdits with no indication of the substitution.

2. No visual indicator: There is no persistent UI element showing the current execution mode. The only way to discover or change it is through the command palette (Cmd+K), and even there the current mode is not highlighted.

3. Undocumented: Execution mode is not mentioned in the README, the mdBook docs, or the arbor.toml reference. Users have no way to learn what it does without reading the source code.

4. Silent no-op for most presets: Only Claude, Codex, and Copilot have mode-specific flag mappings. The remaining 11 presets silently ignore the execution mode with no feedback to the user.

Proposed improvements

1. Visual mode indicator and quick toggle

Add a visible mode indicator to the UI — for example in the preset sub-bar or top bar — showing the current mode (Plan/Build/Yolo) with a click-to-cycle or dropdown behavior. A keyboard shortcut for cycling modes would also help.

2. Show the effective command

When hovering over a preset button or in the preset editor, show the actual command that will be executed after mode flags are applied, not just the raw configured template.

3. Documentation

Add a section to the docs explaining execution mode with a table showing the flag mapping per agent:

Mode	Claude	Codex	Copilot
Plan	--permission-mode plan	-a on-request -s read-only	(no flags)
Build	--permission-mode acceptEdits	--full-auto	--allow-all-tools
Yolo	--dangerously-skip-permissions	--dangerously-bypass-approvals-and-sandbox	--yolo

Clarify that other presets are unaffected by execution mode.

4. Indicate unsupported presets

For presets that don't support execution mode, either grey out the mode indicator or show a note in the preset editor that mode has no effect on this agent.

[Koroqe]

Execution modes controlling permission flags silently is exactly the kind of thing that breaks trust in autonomous workflows. Explicit quality gates where each stage has defined permissions and the user can see what's enforced works much better. https://github.com/Koroqe/claude-code-sdlc