fix(docs): README denies named hub packages and accounts

[Yi-111-a]

Summary

The README limitations list said:

- The hub has no names, versions, accounts or search yet. Packages are hashes.

Three of those four claims are stale against this same tree.

• guide/GUIDE.md:530-532 documents import <name>@<version>/main.bend as P and bend main.bend --publish <name>@<version> after bend login.
• bend2/main.ts implements all of it: bend login writes the Bender key (:67, :133), cli_link calls hub_name (:544-549), --publish <name>@<version> parses a name and runs hub_check (:248-253, :495-539), and the help text already reads "publish the file and its imports; a name needs login" (:41) and "log in to Bender for --publish @…" (:43).

The replacement bullet states what is actually true and keeps the shape of the surrounding limitations:

- A hub package is a hash, unless its author names and versions it after `bend login`.

Fixes #1295.

What I did not change, and why

The original bullet also claimed no search. I dropped that claim rather than restating it: bend2/main.ts has no search verb (grep -c -i search bend2/main.ts → 0), but the hub UI lives in the sibling bend-lang.com checkout named in AGENTS.md, which I could not read, so whether search exists there is not answerable from this repo. #1295 scopes search out separately, so this PR asserts nothing about it. If search does not exist, it is a one-clause follow-up.

Verification

• README.md is 2980 ttok against the permanent 4000 cap in gates/repo.ts:43 (allow("README.md", 4000)), measured with ttok as that gate does. Before: 2977.
• Diff is one line in one file. No code, no gate, no guide/ change — note guide/GUIDE.md is already at 7968/8000 ttok, so I deliberately kept away from it.
• Read README.md, guide/GUIDE.md and bend2/main.ts at a950fd68 (the commit fix(docs): README denies named hub packages and accounts documented by the guide #1295 pins) and again at current main; the stale bullet is unchanged between them, so the report holds against main.
• No build or test run: this is a prose change with no executable surface.

Contract Routing

No contract touched. Documentation-only, outside every gate in gates/ except the README.md ttok cap checked above.