Add a 'squad-commands' skill so users can discover and run common Squad operations from chat #1172

Summary

Add a built-in squad-commands skill that ships with every Squad install. Its job: let the user discover and invoke common Squad operations from chat — without searching docs, without remembering CLI flags, and without typing the raw command.

Today, things like squad upgrade --state-backend git-notes, squad plugin marketplace add, squad watch --interval 5, casting overrides, switching state backends, etc. require the user to either know the flag exists or go googling. That's friction.

User experience (desired)

User says any of:

• "squad commands"
• "what can squad do?"
• "show me squad options"
• "how do I upgrade with state backend"
• "slash commands"

Coordinator presents a categorized, scannable menu (via ask_user with choices, or compact text) of the most common operations. User selects one → coordinator either:

• Runs it directly (for safe / idempotent ops)
• Asks the 1–2 follow-up questions needed (e.g. "which state backend? worktree / git-notes / orphan / two-layer")
• Then executes — no copy-paste of CLI flags required

Skill contents

.squad/skills/squad-commands/SKILL.md should index the operations users actually want, grouped by intent. First pass:

Install & upgrade

• squad upgrade (with optional --state-backend)
• squad init (re-run scaffolding)
• Switch state backend (worktree ↔ git-notes ↔ orphan ↔ two-layer)

Team management

• Add/remove a team member (route to the Adding/Removing Team Members flow)
• Reassign roles
• Show roster / capability profile

Issues & PRs

• Connect a repo (gh auth + GitHub Issues Mode)
• Triage open issues
• Activate Ralph (Ralph, go) / set polling interval
• Start squad watch background poller

Plugins & skills

• squad plugin marketplace add/remove/browse
• List installed skills
• Install a marketplace plugin for an agent

Model & cost

• Set default model (.squad/config.json)
• Override model for one agent
• Clear model preference

Sessions & state

• Catch-up summary
• Show recent decisions
• Archive old decisions / summarize history

Design notes

• The skill is installed as part of squad init — every new squad has it from day one
• Skill confidence starts at high (it's first-party, not earned)
• The skill is discoverable by the coordinator's skill-aware routing — when user intent matches "show me what I can do" / "squad commands" / "help", the coordinator reads this SKILL.md and presents the menu
• The menu is generated from the SKILL.md — no separate code path. Update the markdown, the menu updates.
• For destructive ops (e.g., switching state backend, removing a member), confirm before executing
• Should work across CLI, VS Code, and other Copilot surfaces (no SQL, filesystem-only)

Acceptance criteria

• .squad/templates/skills/squad-commands/SKILL.md exists in the install template
• squad init and squad upgrade install/update this skill into .squad/skills/squad-commands/
• Coordinator routes "what can squad do?" / "squad commands" / "slash commands" / similar intent signals to this skill
• Menu is grouped by category, scannable, and uses ask_user choices where possible
• Selecting an option either runs the command or asks the minimum follow-up questions
• Documented in README so users know it exists
• Works on CLI and VS Code surfaces

Out of scope (for v1)

• Custom user-defined commands (could be a later iteration — read from a user file)
• A separate squad commands CLI subcommand (the skill handles in-chat; CLI can come later)