fix: resolve theme toggle inconsistency across dashboard pages

[nur-hasin]

Which issue does this PR close?

• Closes [bug]: theme toggle not functioning correctly & button UI inconsistent across multiple dashboard pages #1664

Rationale for this change

The theme toggle button was unresponsive or visually broken across multiple dashboard pages. Root causes identified:

• Cursor trail overlay (.circle-container / .cursor-circle) intercepting pointer events and blocking clicks on #themeToggle
• Pages using conflicting theme systems (body.dark-mode class vs data-theme attribute)
• Duplicate click listeners cancelling each other out
• Old toggleTheme() functions in page-specific JS overriding theme.js
• SVG ray <line> elements inside the toggle button intercepting clicks before they reached the button

What changes are included in this PR?

• Added pointer-events: none to .scroll-indicator, .circle-container and .cursor-circle to prevent overlay elements from blocking button clicks
• Added pointer-events: none to theme toggle SVG so ray lines no longer intercept clicks
• Removed duplicate/conflicting toggleTheme() and initializeTheme() functions from app_scheme.js
• Replaced body.dark-mode CSS rules with [data-theme="dark"] selectors in styles_scheme.css to match the unified theme.js system
• Added ../theme.js to pages that were missing it (Gov_schemes/index_scheme.html)
• Removed inline style="position:fixed" from toggle button in main.html navbar
• Applied consistent sun/moon SVG toggle button across all affected pages

Are these changes tested?

Manually tested on all pages in both light and dark mode:

• Verified toggle switches theme on click
• Verified background and card colors change on toggle
• Verified theme persists on page reload via localStorage
• Verified cursor trail no longer blocks button clicks
• Verified no overlay elements block the toggle button
• Tested on Chrome, Firefox, and Edge

Are there any user-facing changes?

Yes - the theme toggle button now correctly switches between light and dark mode on all dashboard pages with smooth sun/moon animation. No visual or layout changes were made.

Screenshots

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[github-actions]

Thanks for creating a PR for your Issue! ☺️

We'll review it as soon as possible.
In the meantime, please double-check the file changes and ensure that all commits are accurate.

If there are any unresolved review comments, feel free to resolve them. 🙌🏼

[nur-hasin]

Hi @omroy07, kindly review and merge if approved. Let me know if any changes are required. Thanks.

[github-actions]

🎉 Congrats @nur-hasin on getting your PR merged! 🙌
Thanks for the contribution — looking forward to more from you 🚀

[nur-hasin]

Hi @omroy07, kindly add the ECWoC26 SPRINT label to this PR. It is necessary for points to be added.

[nur-hasin]

Hi @omroy07, kind reminder - I'd requested the ECWoC26 SPRINT label earlier. Please add it so points can be counted. Thanks.