Inline Codex icons in PageNetworkOptions and fix Title Icon URL

[alistair3149]

Summary

Fixes default group icons (and OOUI Title Icons) 404'ing on wikis with pretty article URLs (/wiki/Foo). The root cause was the same in both call sites: bare relative paths handed to vis-network, which the browser then resolved against the document URL.

• PageNetworkOptions defaults switch to canonical Codex icon names — cdxIconArticle, cdxIconArticleNotFound, cdxIconLinkExternal. A new PHP unit IconResolver looks each name up in MediaWiki's bundled resources/lib/codex-icons/codex-icons.json and emits an inline SVG data: URI in data-options. The lookup tolerates all three icon shapes that the JSON ships (plain string, {ltr, ...}, and {default, langCodeMap, ...}); unknown names log a warning and fall through. Absolute URLs and data: URIs pass through unchanged. Other relative paths get prefixed with $wgScriptPath for backward-compat with users who configured MW-relative paths in LocalSettings.php.
• OOUI Title Icon URL is prefixed with mw.config.get('wgScriptPath') in resources/js/ApiPageConnectionRepo.js (defaulting to '' when unset) so the URL is absolute regardless of article URL style. Title Icon's catalogue is OOUI-style; a Codex migration would need a name-mapping table and per-page user data — out of scope.

The resolver runs after the defaults+user-options merge in NetworkUseCase::getVisJsOptions(), so user-provided per-call options receive the same treatment. Extension::getFactory() reads paths via MainConfigNames::BaseDirectory and MainConfigNames::ScriptPath, no static-analysis suppressions needed.

Test plan

• composer phpunit — 36/36 (was 19; 17 new in IconResolverTest)
• vendor/bin/phpcs -p -s — clean
• vendor/bin/phpstan analyse (level 1) — No errors
• vendor/bin/psalm (errorLevel 2) — No errors found
• Runtime smoke against the local dev wiki — confirmed data-options contains valid data:image/svg+xml;base64,… URIs that decode to real Codex SVGs; icons render in the browser
• CI: all five PHPUnit matrix rows + static-analysis + code-style pass

Out of scope

• Per-group icon colour / theme adaptation. The bundled Codex SVGs render with their default fill (black). Wikis can override per group in LocalSettings.php. Worth a follow-up if the white-card-on-dark-theme look bothers anyone.
• Migrating Title Icon's OOUI icon names to Codex (per-page user data + name-mapping table).
• Refactoring the existing MediaWikiServices::getInstance() service-locator usage in NetworkConfig.