feat: Native Split View (Tab Tiling) Support

[Sameem-baba]

Related Issue (if any)

Closes: #179

Describe the add-ons or changes you've made

Implemented a fully native, persistent Split View architecture for the browser tab bar. This allows users to view two webviews side-by-side while keeping the tab bar UI clean and intuitive.

Core Architecture & Logic:

• Infinite Split Pairs: Upgraded state management (this.splitPairs) to support multiple independent split views simultaneously.
• Context Menu Integration: Added "Split view" and contextual "Separate split view" options.
• State Persistence: Integrated split pair data into getTabsStateForSaving() and restoreTabs() so split groups survive browser restarts and automatically rebuild their DOM structure.

UI/UX & Styling:

• Unified Capsule Design (Vertical Tabs): When in vertical mode, split tabs visually merge into a single "pill" block. When either half is active, the entire capsule highlights with a distinct center divider.
• Seamless Drag & Drop: Rewrote the pointer event engine. If a user drags a split tab, it dynamically wraps both tabs in a dragWrapper so they move as a single unit. Tearing the group outside the container gracefully breaks the split and extracts only the grabbed tab.
• Draggable Resizer: Injected a dynamic .split-view-divider between webviews. Users can drag the seam to smoothly adjust the flex-basis ratio of the left/right panes.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, local variables)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Manual UI Testing: Verified pixel-perfect rendering in both expanded and collapsed vertical tab layouts.
• Drag & Drop: Tested reordering split groups within the tab bar and tearing off individual tabs to new windows.
• Resizer Interaction: Verified that the center divider correctly calculates percentages and smoothly updates the flexbox layout without <webview> iframes swallowing pointer events.
• Session Restoration: Reloaded the browser to confirm localStorage correctly rebuilds the split DOM and restores the custom webview width ratios.

Checklist:

• My code follows the "contribution guidelines" of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly wherever it was hard to understand.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.

[akhileshthite]

Great work!

Keep a note of adding a "Split View" section in Tabs.md after merging #165

[Sameem-baba]

Keep a note of adding a "Split View" section in Tabs.md after merging #165

Yeah! I will keep an eye on that.

[Ayush-Vish]

It would be nice if we could add the reverse views functionality as well
What do you think? @akhileshthite

[akhileshthite]

It would be nice if we could add the reverse views functionality as well What do you think? @akhileshthite

Like swapping the split view? Yeah, we can add that later, not a priority rn.

[Sameem-baba]

It would be nice if we could add the reverse views functionality as well What do you think? @akhileshthite

Yeah! We could add that.

[akhileshthite]

Great work!
Thanks!