Close the username completion and the actions that resolve an account

[JeroenDeDauw]

Fixes #24
Follows-up to #23

Two paths named accounts to members past UserListSpecialPageHandler and UserListApiHandler: username
completion, which bypasses SpecialPage::run(), and top-level API actions, which the API handler never
looked at.

Username completion. The core pages that complete a username — eight in 1.43, Special:Contributions
and Special:UserRights among them — and the extension pages that do the same all declare the
UserNamePrefixSearch service in their special-page list entry and ask it on behalf of the public, paging
through the whole user table; action=opensearch, list=prefixsearch, generator=prefixsearch and
GET /rest.php/v1/search/title, which the search box calls, all arrive there. The extension now rewrites,
in SpecialPage_initList, every entry that declares the service, so the page is built with a wrapper that
answers members with nothing and hands every other search on. Decorating the service from the
MediaWikiServices hook is not an option: that hook never reaches extensions under ProAdmin's loader.php
bootstrap (https://github.com/ProfessionalWiki/ProAdmin/issues/1375). On the dev wiki, under that
bootstrap, all four entry points now return nothing to a member and the names to an ordinary account. Since the
answer now differs by reader, $wgSearchSuggestCacheExpiry is set to 0 on load; it is what marks
action=opensearch and the REST title search publicly cacheable.

API actions. $wgMemberAccessBlockedApiModules, closed to members as before, now refuses top-level
actions as well and ships four: feedcontributions, validatepassword, emailuser and userrights,
each of which names an account or confirms one before any right or token is checked (feedcontributions
and userrights also resolve user=#<id>). A wiki that set the variable gets them too, since array
settings merge. Members lose only the contributions feed: sendemail and createaccount are revoked
already, a member has no password to validate, and no group to grant.

Left open, on purpose: Special:Contributions/<name> and Special:ListFiles/<name> still tell a member
that a name has no account. Each confirms one name at a time, and closing the pages would cost members every
contribution listing and the list of files; a wiki that wants them closed adds them to
$wgMemberAccessBlockedSpecialPages. Whom the roster is hidden from at all is
#26. The #<id> existence answers that remain —
in modules that return no name, and in userrights token validation, which runs before the hook and
answers for a name as well — are
#28.

Considered, omitted: limiting Special:Contributions to the member's own account; naming the completing
pages in the README.

_{AI-authored — Claude Code, Opus 5 (max) diff from a Fable 5 (max) spec for @JeroenDeDauw, redirected once when the first mechanism proved inert under the ProAdmin bootstrap, then adjusted after an independent review pass; diff not yet human-reviewed; both leaks reproduced on a dev wiki before the fix and seen closed after it under that bootstrap, regression tests written first and seen failing, mutations of the wrapper, the page-list rewrite, the wiring and the API handler each caught, every special page on the dev wiki built as member, ordinary account and anonymous visitor, PHPCS, PHPStan and the whole suite run locally, CI green.}

[codecov-commenter]

Codecov Report

❌ Patch coverage is 93.33333% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.98%. Comparing base (d05e3ee) to head (edbd507).

Files with missing lines	Patch %	Lines
src/EntryPoints/UserNameCompletionHandler.php	94.28%	2 Missing ⚠️
src/EntryPoints/RestrictedUserNamePrefixSearch.php	87.50%	1 Missing ⚠️
src/EntryPoints/UserListApiHandler.php	87.50%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #27      +/-   ##
============================================
+ Coverage     86.77%   86.98%   +0.21%     
- Complexity      594      618      +24     
============================================
  Files            67       69       +2     
  Lines          2072     2129      +57     
============================================
+ Hits           1798     1852      +54     
- Misses          274      277       +3     

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[JeroenDeDauw]

Might not do this one, certainly lower priority due to removing the emails from usernames (#29), which removes the main incentive for this PR

[JeroenDeDauw]

Closing unmerged: #29 removed the identity behind every name these paths could return — username completion and the ID walks now yield Member ABC123 forms. What this branch still hides is that members exist and how many, which no requirement asks for and which the merged defences already narrow. The branch stays in place should that ever change.

_{AI-authored — Claude Code, Fable 5 (max); close requested by @JeroenDeDauw in the post-merge cleanup.}