docs(wiki): skill-vs-plugin concept page; flag task-tracking bootstrap gap

- .wiki/concepts/skill-vs-plugin.md: when a bare SKILL.md suffices vs when
  a plugin is required (slash commands, hooks, sub-agents, MCP via
  marketplace). Concrete breakdown of `superpowers` showing why each of
  its non-skill artifacts needs the plugin format.
- .wiki/index.md, log.md: linked / logged.

Backlog: project-bootstrap Step 4 has the same defect as the wiki step
(now fixed in 1cae0a2) — it creates a single flat STATUS.md and never
mentions the per-task files that task-status-wiki actually expects. Added
to .tasks/STATUS.md backlog for a conscious follow-up.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.wiki/index.md

@@ -16,6 +16,7 @@ Catalog of all wiki pages. One line per page, organized by type. Updated on ever
 - [build-notes.md](concepts/build-notes.md) — why `build.ps1` exists alongside `build.sh`; PS 5.1 backslash-in-zip gotcha; how to extract a `.skill`
 - [context7-setup.md](concepts/context7-setup.md) — switched context7 from manual MCP entries to the official plugin; API key in `.mcp.json` as `--api-key`; now also captured as `setup-context7` skill (one-time install/migrate flow with key discovery)
 - [repo-layout.md](concepts/repo-layout.md) — flat `skills/`, committed `dist/`, bash + PowerShell scripts; install model
+- [skill-vs-plugin.md](concepts/skill-vs-plugin.md) — when a bare SKILL.md is enough vs when you actually need a plugin (slash commands, hooks, sub-agents, MCP servers); concrete breakdown of `superpowers`
 - [wiki-realignment.md](concepts/wiki-realignment.md) — fixing `project-bootstrap` to create the Karpathy-canonical wiki layout
 
 ## Packages