Simplify Linear OAuth app setup

[daniel-lxs]

Summary

• include the deployment's Roomote logo in the generated Linear app manifest
• remove the redundant callback and webhook URL fields from the setup dialog
• simplify the copy to refer to Roomote without the self-hosted qualifier

The callback and webhook URLs remain pre-filled in the Linear manifest; users only need to copy the three credentials that Linear cannot return automatically.

Validation

• pnpm exec dotenvx run -f .env.test -- pnpm --filter @roomote/web exec vitest run src/trpc/commands/linear/index.test.ts src/components/settings/Integrations.test.tsx
• pnpm --filter @roomote/web check-types
• pre-push lint, fast typecheck, and knip checks

[roomote-roomote]

No code issues found. See task

_{Reviewed 542f36d}