feat: add tag filtering and task count in navbar

[cyforkk]

Summary

This PR resolves #74 and #75 by adding tag-based filtering and a task count indicator to the DevBoard.

Changes

Issue #74: Show total task count in navbar

• Added a task count badge next to the DevBoard logo in the navbar
• Shows "X tasks" (singular "task" when count is 1)

Issue #75: Clicking a tag should filter board by that tag

• Added state to for tag-based filtering
• Clicking a tag in filters tasks by that tag
• Clicking the active tag again clears the filter
• Active tag is highlighted with a purple ring
• Added an active tag badge in the navbar with a clear button (✕)

Files Changed

• • Added activeTag state and filtering logic
• • Added onClick handler to tags
• • Added task count and active tag badge

Verification

• Task count displays correctly in navbar
• Clicking a tag filters tasks by that tag
• Clicking the active tag again clears the filter
• Active tag is visually highlighted
• Clear button (✕) removes the tag filter

[anoopcodehack]

Thanks for the contribution!
Great work implementing both features in a single PR. The task count in the navbar and the tag-based filtering improve the overall usability of the board, and I appreciate the clear summary and verification steps.
I'll merge this PR shortly. Thanks for contributing!