Add clickable button to filter issues and PRs

[bipplane]

Summary:

Fixes #496
Add clickable header buttons for issues and PRs. This allows for unrestricted account-based filtering of issues/PRs, while also improving usability by reducing the number of clicks and mouse movements needed for filtering.

Type of change:

• ✨ New Feature/ Enhancement

Changes Made:

• Added issue type filtering logic instead of leveraging on the existing filter to prevent introducing bugs to the original state filter.
• Issues or PRs with a count of 0 will not be allowed to be filtered.
• Added hover state, active state, inactive state CSS styling to the buttons

Screenshots:

Before

To look at only one type of card, you would need to go into status and tick/untick the respective boxes.

WATcher.1.4.1.-.AY2425S2-CS2103T-T16-4_tp.-.Google.Chrome.2025-07-17.23-13-03.-.Trim.mp4

After

Now, you can just click to see whichever type of card on each user.
Note: this will be able to work alongside the original status filter.

WATcher.1.4.1.-.AY2425S2-CS2103T-T16-4_tp.-.Google.Chrome.2025-07-17.23-13-47.-.Trim.mp4

Proposed Commit Message:

Adds the ability for users to filter cards by type (issue or PR) 
directly from the card view headers.

Clicking the issue or PR count toggles a filter to show only 
items of that type. Clicking the active filter again reverts this 
filter back to the original state.

This enhancement provides a more responsive, one-click method 
for filtering, which is especially useful in high-volume scenarios 
such as the huge influx of issues during PE-D or actual PE.

Checklist:

• I have tested my changes thoroughly.
• I have created tests for any new code files created in this PR or provided a link to a issue/PR that addresses this.
• I have added or modified code comments to improve code readability where necessary.
• I have updated the project's documentation as necessary.

[NorbertLoh]

Some things to think about:

• do we need a clear all or a way to reset such that users do not have to manually deselect all
  • for example when user filters by pr -> filter by status, should it reset?
• could we make the icon change colour as well to follow the number
• perhaps we could prevent highlighting of the number to make it cleaner

[NorbertLoh]

LGTM! I quite like this feature 👍. Maybe for future implementations, we can clear the filters when the overall filter changes