refactor(wiki): migrate this repo's .wiki/ to canonical Karpathy layout

Stop being inconsistent with our own fixed project-bootstrap template.

- SUMMARY.md → index.md (catalog by type, with one-line hooks)
- source/*.md → concepts/*.md (with `git mv` so history is preserved)
- WORKFLOW.md removed (workflow lives in wiki-maintainer, not duplicated here)
- New: .wiki/CLAUDE.md (project schema, Karpathy gist URL pinned at top)
- New: log.md (append-only op log; backfilled with prior decisions)
- New: overview.md (single project intro page)
- New: raw/README.md (immutability note; replaces .gitkeep placeholder)
- Empty .gitkeep added to entities/, packages/, sources/
- Migrated pages got `type: concept` frontmatter

After this, wiki-maintainer reads .wiki/CLAUDE.md → index.md as it expects,
and the layout matches what newly-bootstrapped projects will look like.

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

.wiki/raw/README.md

@@ -0,0 +1,13 @@
+# Raw Sources
+
+**Immutable.** Read, never edit. The only allowed modification is appending a `> Status:` blockquote when the user explicitly asks for a status audit.
+
+Place raw inputs here — articles, transcripts, PDFs, screenshots — exactly as they came in. The agent reads from `raw/`, writes summaries into `../sources/`, and never modifies raw files.
+
+For large or path-sensitive sources outside the repo, register them here:
+
+```
+- short-name → /absolute/path/to/source
+```
+
+Currently: no raw sources yet.