Add frontend-extensibility probes to RedHerb

[malberts]

Result of extensive back-and-forth with @malberts.
Context: the NeoWiki codebase and live browser verification of every integration point.
_{Written by Claude Code, Opus 4.7 (1M context)}

Follows-up to #754

Adds three RedHerb sidebar entries that act as permanent integration probes for the JavaScript extension surface introduced by #754. RedHerb (tests/RedHerb/) is NeoWiki's in-tree extension whose purpose is to be a working example of how to consume NeoWiki's extension points; everything in it lives alongside the codebase as ongoing validation. The entries are deliberately contrived — they are not user-facing features and a real extension would build a different UI on top of the same primitives — but they exercise concrete pieces of the public-API barrel end-to-end.

What the probes do

• Find a subject is always present. Routes to a new Special:RedHerbSubjectFinder page where a panel lets the user pick a subject by schema and label, then renders the selected subject using NeoWiki's Infobox view component.
• Create child Company is shown on every existing wiki page. Opens a RedHerb-owned dialog pinning the Company schema and reusing NeoWiki's SubjectEditor. On save it calls subjectStore.createChildSubject through the shared Pinia, persisting the new child via the SubjectRepository REST path.
• Edit main subject is shown only on pages that already have a main subject — the sidebar hook calls NeoWikiExtension::newViewHtmlBuilder()->pageHasMainSubject() to decide (RedHerb's first PHP-side runtime API consumption). Click opens a RedHerb-owned dialog wrapping SubjectEditor pre-populated with the existing main subject's statements. On save it calls subjectStore.updateSubject, and NeoWiki's existing Infobox on the same page reactively re-renders without a reload.

Integration points exercised through the public-API barrel

Surface	Used here
Shared Pinia owned by NeoWikiExtension	Cross-boundary mutation observed empirically (creator dialog opens; child subject persists; main-subject edits flow back into NeoWiki's Infobox without reload)
Reactive view sync across the boundary	RedHerb mutates a Subject via subjectStore.updateSubject; NeoWiki's Infobox on the same page re-renders live, proving the shared store drives reactivity end-to-end
REST repositories	RestSubjectLabelSearch via the embedded SubjectLookup; RestSubjectRepository via subjectStore.createChildSubject (POST) and subjectStore.updateSubject (PATCH) and StoreStateLoader. The other repos in the barrel use the same import chain and HttpClient, so exercising more is more of the same coverage.
Application services	SubjectLabelSearch, PropertyTypeRegistry, SubjectAuthorizer (transitively via SubjectEditor/Infobox)
Pinia stores	useSubjectStore (read + create + update), useSchemaStore
Vue components	SubjectLookup, Infobox, SubjectEditor
Vue.createMwApp from RedHerb	Three RedHerb-owned mounts, each with app.use( ext.getPinia() ) and NeoWikiServices.registerServices( app )
PHP-side runtime API	NeoWikiExtension::newViewHtmlBuilder()->pageHasMainSubject() consumed by RedHerbSidebarHook to gate the conditional Edit link
MW SidebarBeforeOutput hook	New RedHerbSidebarHook
MW NeoWikiGetFrontendModules hook	New RedHerbFrontendModulesHook adds the global RedHerb modules on every NeoWiki page
MW SpecialPage registration	New Special:RedHerbSubjectFinder

Cross-boundary Pinia sharing recipe

1. Visit any content page that has a main subject (e.g. ACME Inc).
2. Click Create child Company in the RedHerb sidebar section.
3. Fill in the dialog (Label, optional Status etc.) and submit.
4. The dialog closes and the new child appears on ?action=subjects for the same page.

The dialog and subjectStore.createChildSubject are owned by separate Vue apps mounted by RedHerb and by NeoWiki respectively. They observe the same store because they share a Pinia instance owned by NeoWikiExtension (the singleton routing was added to #754).

Screenshots

• Sidebar links:

* Sidebar entries on a content page, dialog open showing `SubjectEditor` for Company: * Subjects action page showing the persisted child after save: * `Special:RedHerbSubjectFinder` lookup with `Infobox` rendering of the selected subject: