tesks-ui: Integrations screen — split into API/MCP vs Integrations under settings accordion, fix card width/alignment

Integrations structure is broadly okay but stylistically off and misaligned.

• Split it into API / MCP vs Integrations, surfaced under the new settings accordion (see Navbar issue): API keys/MCP in one section, third-party integrations (Discord, GitHub) in another.
• The cards are pushed off to the left and use a different width/layout from the rest of the app — align them to the shared page container + card styling.
• General stylistic polish of IntegrationCard / ApiKeys.

Files: app/(app)/w/[workspace]/integrations/*, components/IntegrationCard, components/ApiKeys. Commit to develop, ref this issue.