Gate debug control UI behind runtime env flag

[becktothefuture]

Motivation

• Prevent debug-only controls and routes from appearing in production by gating them behind a runtime toggle.
• Give developers an easy way to re-enable the controls locally for debugging without changing code or shipping debug affordances to users.

Description

• Added a runtime flag isDebugUIEnabled in src/App.jsx using import.meta.env.DEV || import.meta.env.VITE_ENABLE_DEBUG_UI === 'true' and used it when initializing and reading app view state.
• Guarded all control entry points so they are no-ops or hidden when the flag is false: the floating launcher, inline control dock, external portal mount, / key handler, and the quick navigation actions between Depth Lab and Typography Lab.
• Hardened routing so readAppView and runtime view changes ignore debug-only views when debug UI is disabled, and the app will force the view back to home if needed.
• Added a root attribute sync (document.documentElement.dataset.debugUi) and a CSS safety net in src/styles.css that keeps .eli5-control-launcher and .eli5-control-dock hidden unless html[data-debug-ui='true'] is set.
• Added docs/development.md documenting the env switch and the local command to enable debug UI (VITE_ENABLE_DEBUG_UI=true).

Testing

• Ran a production build with npm run build and it completed successfully.

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[chatgpt-codex-connector]

Re-enable control dock when debug UI is active

This change hides .eli5-control-dock by default, but the debug override only restores width and never restores display, so the inline dock remains invisible even when debug UI is enabled. In practice, that breaks the fallback path where controls should appear in-page (for example when the popup window cannot open), leaving debug controls inaccessible in dev/debug sessions.

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