Change README title to Sidekick app extensions intent types

[adambarrus]

Updated the title of the README to reflect the focus on Sidekick app extensions.

Proposed type

• Type: application/...
• Actions: create / edit / both
• One-line summary:

Why this type

What merchant intents does this capture? Real examples beat hypotheticals.

Who would register intents for it

Apps you've talked to (yours plus others), or app categories you'd expect to register.

Schema sketch

Either a JSON Schema fenced below, or a link to a Gist / branch / external schema.

{
}

Confirmed:

• inputSchema does not declare required fields
• Field names are consistent with neighboring types in types/

Prior art

Existing types this is closest to, and why a new type rather than extending one of them:

Anything else

Open questions, things you're unsure about, areas where you'd especially like reviewer input.