Add two major feature areas on top of the MuPDF Android viewer base.

### E-ink Screen Optimizations

- Add `setAnimationsEnabled(bool)` to ReaderView: when disabled, scroll
  duration drops from 400 ms to 1 ms and drag scrolling is suppressed,
  eliminating ghosting on e-ink panels.
- Add `setEinkRefreshEnabled(bool)` to ReaderView: posts an invalidate()
  after each page settlement to trigger a full-screen refresh cycle.
- Fling gestures now jump directly to the next/previous page instead of
  smooth-scrolling when animations are off.
- Add a Settings button (wrench icon) to the top bar with a popup menu
  for toggling animations, e-ink refresh, and setting the OpenAI API key.
  All settings are persisted via SharedPreferences.

### AI-Assisted Reading

- Add AiDocumentActivity (extends DocumentActivity) that overlays a
  Jetpack Compose UI onto the existing PDF reader without replacing it.
- Add IonizationOverlay: a full-screen Canvas gesture layer that detects
  free-form draw gestures and fires a vibration + AI request on release.
- Add OpenAiClient: streams chat completions from the OpenAI API over SSE
  using OkHttp. The system prompt produces two structured sections —
  an AI Explanation and an Atomic Note (core concept / key insight /
  connections).
- Add AiPanel: a bottom sheet built in Compose that slides up and renders
  the streaming response token-by-token in real time.
- Expose MuPDFCore.getPageText() to extract structured text from the
  current page via MuPDF's StructuredText API for use as AI context.
- Add SecurePreferences: stores the OpenAI API key in
  EncryptedSharedPreferences (AES256-GCM) so the key is never stored
  in plain text.
- Add ObsidianExporter: saves AI responses as Markdown files under
  Documents/ObsidianVault/Atoms/ with #atom #atomread tags for
  integration with Obsidian.
- Add AtomReadActivity registered as an alternate PDF intent handler
  (application/pdf MIME), combining the PDF viewer with the AI overlay.
- Add BondingView: prototype Compose component for visually linking
  atomic notes via drag-and-drop collision (not yet wired to main flow).