feat: split wiki — using-wiki (policy) + setup-wiki (one-time)

Rename `wiki-maintainer` to `using-wiki` (rename via git mv preserves
file history). Strip greenfield/bootstrap content out of it; add a
Prerequisites section that delegates to the new `setup-wiki` skill when
`.wiki/` is missing or non-canonical.

New `setup-wiki` skill: 6-phase procedure (sanity → discovery → plan +
confirm → backup → create/migrate → verify → report). Two modes —
greenfield (no `.wiki/`) and migrate (existing non-canon, e.g. SUMMARY.md
+ source/). Confirmation gate before any write. Templates for each canon
file (`CLAUDE.md` schema, `index.md`, `log.md`, `overview.md`,
`raw/README.md`) baked in.

`project-bootstrap` Step 3 now delegates to `setup-wiki` instead of
holding inline templates that drift from canon.

After this commit, `~/.claude/skills/wiki-maintainer/` still exists as a
stale install — the user will rm it manually after commit (c) lands the
tasks split.

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

.wiki/log.md

@@ -23,3 +23,4 @@ Parseable: `grep "^## \[" .wiki/log.md | tail -20`.
 ## [2026-04-28] verify | setup-context7 — Vitya ran using-context7 in a session that needed setup; Prerequisites pointer triggered setup-context7; full flow worked end-to-end. Pattern (policy + setup split) validated.
 ## [2026-04-28] decision | skill-vs-plugin — documented when a bare skill suffices vs when a plugin is required (slash commands, hooks, sub-agents, MCP via marketplace)
 ## [2026-04-28] decision | skill-versioning — added `version: 1.0.0` to 6 infra skills' frontmatter; project-bootstrap now writes .wiki/concepts/bootstrap-manifest.md per project
+## [2026-04-28] refactor | wiki split — `wiki-maintainer` renamed to `using-wiki` (policy); new `setup-wiki` skill owns greenfield creation and canon migration; `project-bootstrap` Step 3 delegates