docs: fix broken documentation link in README - #1636

The "Usage" section links to
https://docs.withampersand.com/v1.0/docs/embeddable-ui-components
which returns 404.

The /v1.0/docs/ path prefix predates the docs migration to Mintlify,
which serves the page at the bare path. The rest of the repo already
uses the current form, e.g. src/headless/config/useConfigHelper.tsx
links to /write-actions and generated-sources links to
/embeddable-ui-components.

Updated to https://docs.withampersand.com/embeddable-ui-components
(verified 200). This was the only /v1.0/docs/ reference left in the
repo.

Two other documentation links also 404, but they are left alone here
because they live in generated SDK code and would be overwritten by the
next regeneration -- they likely need fixing in the OpenAPI spec
upstream:

  https://docs.withampersand.com/reference/oauth/get-url-for-oauth-flow
    generated-sources/api/src/apis/ConnectionApi.ts:118,129,289,327

  https://docs.withampersand.com/reference/provider-apps/create-provider-app
    generated-sources/api/src/models/OauthConnectRequest.ts:78

All other docs.withampersand.com links in the repo were checked and
resolve: /cli/overview, /embeddable-ui-components, /headless,
/write-actions, /reference/connection/list-connections and
/reference/oauth/generate-oauth-authorization-url.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>