show surrounding text context on manual pause and fix programmatic pause loop

[fran-jag]

Description
This PR enhances the reading experience by providing surrounding text context whenever the user
manually pauses the reader. It also includes a fix for the "Pause every N words" feature
and adds a new setting to toggle the context view.

Key Changes

1. Context View on Pause (Feature)

• When the reader is manually paused (via Space or the Pause button), the display now shows up to
  60 words of context (previous and next) around the current word.
• The context is styled in a light gray tone with a smaller font to maintain focus on the current
  word while providing broader situational awareness.
• Updated the layout to support multi-line wrapping for the context words, ensuring a clean and
  readable "paragraph" feel during breaks.

2. Settings Integration

• Added a new toggle in the Display section of the Settings panel: "Show context when paused".
• This allows users to opt-out of the context view if they prefer the traditional minimal RSVP
  interface.
• The setting is persisted in the browser's local storage along with other session data.

3. Bug Fix: Programmatic Pause Loop

• Fixed a bug where the "Pause every N words" feature would enter an infinite loop or cause the UI
  to "flash/stuck" because the pause trigger was checked before the word index was incremented.
• Refined the logic to ensure that programmatic pauses do not trigger the context view, preserving
  the reading rhythm for automated breaks.

4. UI Refinements

• Multi-word Mode Compatibility: Ensured that "Words shown simultaneously" are hidden when the
  paused context is active to prevent word duplication on screen.
• RTL Support: Maintained compatibility with Right-to-Left (RTL) scripts for the new context
  layout.

Technical Details

• src/App.svelte: Introduced isManualPause state to distinguish between user-triggered pauses
  and automated ones. Updated derived states for contextBefore and contextAfter.
• src/lib/components/RSVPDisplay.svelte: Updated CSS and template logic to handle flexible
  container heights and multi-line text wrapping when showContext is active.
• src/lib/components/Settings.svelte: Expanded the UI to include the new toggle.

Testing Performed

• Verified manual pause triggers context correctly.
• Verified "Pause every N words" resumes playback as expected without showing context.
• Tested toggle functionality in Settings.
• Confirmed that multi-word mode does not clash/duplicate text when pausing.
• Verified session saving/loading preserves the new setting.