Add /list-slash-commands for workspace command discovery

[V0latix]

Context

Users currently need to know slash command names in advance. This change adds an explicit discovery command for commands that are actually introspectable from this repository/workspace.

Problem

There was no dedicated command to list currently detectable slash commands in the active workspace. This hurts discoverability, especially for project and plugin commands.

Solution

• Add local slash command /list-slash-commands.
• Add scripts/list-slash-commands.sh as a single collection/normalization point.
• Detect and display commands from:
  • .claude/commands (Project)
  • plugins/*/commands (Plugins)
• Output is stable and sorted:
  • grouped by source (Project, then Plugins)
  • sorted by command name within each group
  • includes name, source, description, usage (from argument-hint), and origin
• Robustness behavior:
  • command does not fail if some sources are unavailable
  • emits note: Some command sources could not be introspected.
• Hardening included:
  • robust plugin manifest parsing (python3 with jq fallback)
  • fallback to plugin directory name when manifest is invalid/unavailable

Scope and honesty

This command reports detected slash commands in current workspace. It does not claim to list all runtime Claude Code commands (for example built-ins or non-introspectable MCP-backed runtime commands).

Tests

Added scripts/test-list-slash-commands.sh covering:

• empty result set
• project command detection
• plugin command detection
• stable output/sorting
• unavailable source tolerance (no crash)
• invalid plugin manifest fallback + warning

Run:

bash scripts/test-list-slash-commands.sh

Documentation

Updated README with a short Local slash command discovery section documenting both supported sources and explicit non-guarantees.