refactor(ui): simplify and validate items-per-page input handling

[luannmoreira]

Description:

This PR refactors how the itemsPerPage value is handled in the DataTable component to simplify state management and improve user input validation. Key changes include:

Refactors

• Removed unnecessary v-model and internal state tracking for itemsPerPage
• Replaced outlined and center-affix props with cleaner input markup
• Introduced explicit parsing, clamping, and error messaging for invalid values
• Reset page to 1 only when the value changes meaningfully
• Simplified event handling (@blur, @keydown.enter, etc.)

Tests & Snapshots

• Updated unit test descriptions for clarity (via combobox selection)
• Adjusted all affected snapshots to reflect new rendered DOM
• Ensured form validation behaves as expected across views

Affected Areas

This change impacts all components and views using the DataTable with pagination, including:

• DeviceList
• UserList
• NamespaceList
• SessionList
• PublicKeyList
• Tags, Connectors, Containers, and related pending/rejected views

Why?

• Reduce unnecessary complexity from dual v-model bindings
• Improve robustness of numeric input handling
• Prevent invalid values and make validation UX clearer