feat: floating quick-access toolbar for sync commands

[swapnilsubhashpatil]

Closes #48

Summary

Adds an optional floating toolbar for quick access to the sync commands
without opening the command palette. It's a single draggable button pinned to
the right edge of the app that expands into a menu of sync actions.

Disabled by default — fully opt-in.

Screenshots

Collapsed	Expanded menu	Settings

What it does

• Toggle in settings (Floating toolbar) shows/hides it live, no reload needed.
• Draggable button on the right edge — drag it vertically to reposition; a
  press without movement opens/closes the menu.
• Expandable menu with the four sync actions: Push, Pull, Fix paths, Reset.
  The button shows the sync icon when collapsed and a cross when open.
• Opens away from the edge — if dragged near the top, the menu opens below
  so it never runs off-screen.
• Choose which actions appear under a Toolbar actions sub-group (shown only
  when the toolbar is enabled). At least one action must stay enabled; default is
  Push.
• Buttons call the existing push / pull / fixDrivePath / reset helpers and
  no-op while a sync is in progress.

Implementation notes

• Native styling throughout: Obsidian CSS variables (--interactive-normal,
  --background-secondary, --background-modifier-border, etc.), setIcon for
  Lucide icons, and aria-label tooltips.
• The launcher icon is registered via addIcon('ogd-sync', …) — a Lucide
  refresh-cw scaled to Obsidian's icon grid, so it recolors with the theme.
• Responsive down to mobile widths; drag works with touch (touch-action: none).
• Cleanly torn down on unload and when disabled (element removed, document
  listener detached) — no leaks.

Tests

• Added tests/floating_toolbar.test.ts covering action selection (only enabled
  actions returned, in order; icon/label mapping; empty when all disabled),
  matching the existing test style.
• npm test → all passing. npm run build and npm run lint clean.

Docs

• README: added a Features bullet and a Use entry describing the setting.

Changes

• main.ts — setting + toolbar create/drag/toggle/teardown, per-action toggles,
  at-least-one enforcement
• styles.css — toolbar styles
• tests/floating_toolbar.test.ts — action-selection tests
• README.md — docs