feat(skills): filter install skill client dropdown to supports_skills clients

[samuv]

The install skill dialog showed all installed clients in the client dropdown, including clients that don't support ToolHive skill installation.

• Filter the client dropdown in DialogInstallSkill to only include clients where supports_skills: true, using the new field added in Add supports_skills to GET /api/v1beta/discovery/clients response toolhive#4699
• Update the discovery clients mock fixture to include supports_skills on all entries, with true for claude-code, opencode, and codex
• Add a test asserting that non-skill-supporting clients (cline, cursor, vscode, etc.) are excluded from the dropdown

[Copilot]

Pull request overview

This PR updates the Skills “Install skill” dialog to only offer clients that actually support ToolHive skill installation, aligning the UI with the new supports_skills field from the discovery clients API.

Changes:

• Filter the install-skill client dropdown to only include installed clients where supports_skills is true.
• Update the discovery clients mock fixture to include supports_skills for all client entries.
• Add a UI test asserting only skill-supporting clients appear in the dropdown.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
renderer/src/features/skills/components/dialog-install-skill.tsx	Filters discovered installed clients to those with supports_skills: true before populating the Select.
renderer/src/features/skills/components/__tests__/dialog-install-skill.test.tsx	Adds a test that verifies non-skill-supporting installed clients are excluded from the dropdown.
renderer/src/common/mocks/fixtures/discovery_clients/get.ts	Extends the default mock discovery client list with supports_skills flags for each client.