feat: Add onboarding tour triggered after first patch

[MarcaDian]

• Tour prompt dialog shown after the first successful patch install; appears after the notification permission dialog closes if one was shown
• Multiphase coach-mark overlay across 13 steps in 3 phases: Home → Sources sheet → Settings
• Spotlight cutout with pulsing animation highlights each UI element
• Smooth fade-in entrance on overlay appearance
• Animated card position - slides between top/bottom based on highlighted element location
• Back button in the card and system Back key step backward through the current phase; reaching step 0 of a phase restores the previous screen or sheet before resuming the prior phase
• Overlay is hidden during phase transitions to prevent ghost elements while navigating between screens
• Each step automatically scrolls and navigates to its target — Settings tabs switch and scroll positions animate so the highlighted element is always in view
• Sources sheet phase renders the overlay inside a separate Dialog window so it appears above the ModalBottomSheet's own popup layer
• Coach-mark card is width-capped and position-clamped to remain fully on screen at any screen size and orientation
• Swipe gesture hint stops immediately when advancing to the next step
• Feature tour entry in Settings → System → About lets the user replay the tour at any time after the initial run

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