[Dev UI] Migrate Tool request/response components to expansion panel pattern

[MichaelDoyle]

Description

Currently, <code-block> and <reasoning> components in the Genkit Developer UI are implemented using <mat-expansion-panel> with the shared rendered-block-expansion-panel mixin. This gives them:

• Collapsible body panels (collapsible on click/keyboard for long snippets)
• Standardized header typography and padding
• A copy-to-clipboard action button in the header

In contrast, <tool-request> and <tool-response> components are implemented using plain <div> containers (.toolrequest-container, .toolresponse-container) with bespoke header markup. As a result:

• They cannot be collapsed when tool request/response JSON payloads are large.
• They lack a copy button in the header to easily copy tool inputs/outputs.
• Their styling requires duplicated SCSS rather than inheriting the shared expansion panel mixin.

Proposed Changes

1. Refactor to <mat-expansion-panel>:

   • Update tool-request.component.html and tool-response.component.html to use <mat-expansion-panel [expanded]="true">.
   • Use <mat-expansion-panel-header> to house the tool name, reference ID chip (#ref), tooltip, and action buttons.

2. Add Header Actions:

   • Add a Copy button (<button mat-icon-button matTooltip="Copy">) to copy the highlighted/formatted JSON payload to clipboard.

3. Style Consolidation:

   • Apply the mixins.rendered-block-expansion-panel() mixin to tool-request.component.scss and tool-response.component.scss, removing redundant custom container styling and aligning all message blocks into 100% architectural and visual parity.