feat: name a new account account-N and ask for the name instead of naming it after the provider

What to build

A shell that creates an account no longer names it after the software. wso2 <namespace> connect <url> today names a new account after the product descriptor's provider string, so a Thunder deployment becomes an account called thunder, wso2 whoami reports Account thunder, and a second Thunder server collides on the same name. wso2 login --url <issuer> has the same shape of problem from the other direction: it names the account after the issuer host.

Both paths should instead fall back to the next free account-N (account-1, account-2, …), and should ask for a name when they are allowed to ask. The prompt reads Account name [account-1]:, Enter accepts the default, and a name that is invalid or already taken is asked again rather than refused — a person who typed a name that is already in use should be able to type another without re-running the command. When nothing may prompt (--no-input, WSO2_NO_INPUT, or standard input is not a terminal) the default is taken silently, so scripts and CI never hang.

An explicit --account <name> keeps behaving exactly as it does now, including the refusal when that name is already taken: the user named something specific, and quietly renaming it would be the shell overriding them.

wso2 login --url <issuer> must stay idempotent. It reuses an account of the derived name today, so re-running it against the same issuer does not pile up accounts. With a numbered default, that reuse has to be found by the issuer and client the account already authenticates against; only when no account matches does the login allocate a new account-N.

The same-named context keeps following the account name, as it does now.

Acceptance criteria

• wso2 <namespace> connect <url> with no --account and nothing to prompt creates account-1 on an empty document, and the next free number when lower ones are taken.
• wso2 login --url <issuer> with no name given behaves the same way, and reuses an existing account that already authenticates against that issuer with that client instead of allocating a new number.
• When a prompt is allowed, both paths ask Account name [account-1]: on standard error, and Enter accepts the default.
• A name entered at the prompt that fails the context-document name rule, or that is already taken by an account or a context, is asked again.
• --no-input, WSO2_NO_INPUT, and a standard input that is not a terminal each take the default without asking.
• --account <name> naming an account that already exists is still refused, with the recovery it gives today.
• The connect and login reports say the name was assigned and name --account <name> as the way to choose one.
• docs/reference/commands.md and docs/guides/login.md describe the new naming; the command synopsis near the top of commands.md matches.

Blocked by

• None — can start immediately.

Start with the connect and login command entry points and the account/context document handling, then read the existing naming, prompting, and issuer-matching flows. Use the acceptance criteria to check numbered allocation, interactive and non-interactive behavior, explicit-name errors, idempotent login, and reports. Update docs/reference/commands.md and docs/guides/login.md, including the commands synopsis.