fix(explore): update browser tab title to show chart name

[dganesh05]

SUMMARY

This PR fixes the browser tab title not updating when opening charts in Explore view. Previously, the tab title remained generic even when viewing a specific chart, making it difficult to identify which chart is open when multiple tabs are present.

Changes:

• Added originalDocumentTitle constant to capture the default title at module load
• Implemented useEffect hook in ExploreViewContainer to update document.title when sliceName prop changes
• Added cleanup function to reset title when component unmounts or when navigating away

Design Decisions:

• Follows the same pattern used in DashboardPage.tsx for consistency
• Updates title reactively based on props.sliceName from Redux state
• Handles edge cases: unsaved charts (null sliceName), chart name changes, and navigation cleanup
• No breaking changes - purely additive functionality

Fixes #7

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Before: Browser tab shows generic "Superset" title even when viewing a specific chart.

After: Browser tab displays the chart name (e.g., "Sales by Region") when viewing a chart in Explore view.

TESTING INSTRUCTIONS

1. Test chart title update:

   • Navigate to Superset and open an existing chart in Explore view (/explore/)
   • Verify the browser tab title displays the chart's name
   • Open a different chart in a new tab
   • Verify the new tab shows the second chart's name

2. Test title reset on navigation:

   • While viewing a chart, navigate away (e.g., go to home page or dashboard list)
   • Verify the tab title resets to the default "Superset" title

3. Test unsaved charts:

   • Create a new chart (unsaved chart with no name)
   • Verify the tab title remains at the default title

4. Test chart name changes:

   • Open a chart and verify the title shows the chart name
   • Edit the chart name (if you have permissions)
   • Verify the tab title updates to reflect the new name

5. Verify dashboard titles still work:

   • Open a dashboard and verify its title appears in the tab
   • Navigate away from the dashboard
   • Verify the tab title resets to "Superset"

ADDITIONAL INFORMATION

• Has associated issue: Fixes Issue #4 - [BUG] SQL Lab not displaying string values with angle brackets #7
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API