feat: add Connector Gateway UI and MCP wiring

[4pmtong]

Related Issue

Closes #

Description

Adds the first Eigent-side Connector Gateway integration.

Introduce a generic Connector Gateway UI and wiring for hosted connector runtimes, while keeping the frontend/backend naming provider-agnostic so we are not tightly coupled to OpenConnector long term.

Changes include:

• Adds Connector Gateway API client and server capability detection.
• Adds the Connector Gateway view under Connectors, including provider listing, search/pagination, connector detail drawer, connection state, and action previews.
• Gates Connector Gateway UI by server capability so it only appears when connected to an Eigent server that supports connectors.
• Adds chat store wiring so Connector Gateway MCP config can be mounted into new tasks.
• Updates agent prompts across agent types to prefer MCP tools when users ask to query or operate connected third-party apps.
• Keeps connector execution behind the hosted eigent_server Connector Gateway instead of calling connector providers directly from desktop.

Testing Evidence (REQUIRED)

• I have included human-verified testing evidence in this PR.
• This PR includes frontend/UI changes, and I attached screenshot(s) or screen recording(s).
• No frontend/UI changes in this PR.

Testing performed:

• Ran frontend type check locally.
• Verified Connector Gateway renders provider list from eigent_server.
• Verified connector detail view shows metadata and available actions.
• Verified connected connector tools are available to a new chat task through the Connector Gateway MCP config.
• Verified the UI is hidden/disabled when the server does not advertise Connector Gateway support.

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Contribution Guidelines Acknowledgement

• I have read and agree to the Eigent Contribution Guideline

Notes for Reviewers

This PR depends on the companion eigent_server Connector Gateway deployment/configuration. The desktop app should not talk to OpenConnector directly; it only consumes eigent_server connector APIs and MCP config.