Move development scripts into development/, leaving scripts/ plugin-only

The root scripts/ folder now holds only download_bin.vim, the one script
the plugin itself invokes (via :NuwikiInstall and the vim-plug/Dein build
hooks). All developer tooling — the start-nvim/start-vim launchers,
test-personal-wiki, the keymap harnesses, and syntax-diag — moves to
development/ alongside the developer docs.

REPO_ROOT resolution is unchanged (development/ sits one level under root,
same as scripts/ did); only the explicit cross-references, the CI harness
invocations, the README launcher paths, and the ONBOARDING structure tree
are updated.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

development/ONBOARDING.md

@@ -65,9 +65,21 @@ nuwiki/
 ├── doc/                        # Vim help documentation
 │   └── nuwiki.txt
 │
-├── scripts/
+├── scripts/                    # Plugin-runtime scripts only
 │   └── download_bin.vim        # VimL binary download (used by Dein/vim-plug build hooks)
 │
+├── development/                # Developer-only tooling and docs (not shipped)
+│   ├── ONBOARDING.md           # This file
+│   ├── nuwiki-architecture.html
+│   ├── start-nvim.sh           # Launch Neovim against a scratch wiki
+│   ├── start-vim.sh            # Launch Vim against a scratch wiki
+│   ├── test-personal-wiki.sh   # Launch Vim against your real wiki
+│   ├── test-keymaps.sh         # Neovim keymap harness (CI)
+│   ├── test-keymaps.lua
+│   ├── test-keymaps-vim.sh     # Vim keymap harness (CI)
+│   ├── test-keymaps-vim.vim
+│   └── syntax-diag.vim         # Dump highlighting state for debugging
+│
 └── .gitea/
     └── workflows/
         ├── ci.yaml             # Lint, test, fmt check on every push/PR