Scaffold StepForge: docs, license, audit, npm project

- Environment audit and stack decision in build/agent_audit.md
  (Node + Electron shell over dependency-free core; deviation recorded)
- Rewrite README/ARCHITECTURE/CONTRIBUTING for StepForge
- Add SECURITY.md threat model, CODE_OF_CONDUCT.md, CHANGELOG.md, MPL-2.0
- Replace template grep checks with structural workflow check

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -0,0 +1,27 @@
+# Changelog
+
+All notable user-visible changes are recorded here. The format follows
+Keep-a-Changelog conventions; versions follow semver.
+
+## [0.1.0] - 2026-06-10
+
+Initial release.
+
+### Added
+
+- Guide library with folders, favorites, title + full-text search, and a
+  quick-actions palette.
+- Capture engine: full-screen / active-window / region capture, delay,
+  pause/resume, global hotkeys, click markers, clipboard paste, image import.
+- Three-pane editor: step tree with substeps, statuses, hidden/skipped steps,
+  focused view, autosave, undo/redo.
+- Annotation canvas: rect, oval, line, arrow, text, tooltip, numbered marker,
+  blur, highlight, magnify, crop; normalized JSON scene graph.
+- Rich text descriptions, informational text blocks, code blocks, tables,
+  step links, and placeholders (global / guide / system scope).
+- Single-file `.sfgz` share archives, linked guides with lock files,
+  snapshot backups and restore.
+- Exporters: JSON, Markdown, Simple HTML, Rich HTML, PDF, animated GIF,
+  image bundle, DOCX, PPTX; per-format templates shareable as `.sfglt`.
+- System/light/dark theming, keyboard shortcuts, settings dialog.
+- Offline guarantee: zero network code paths.