Story Share portal: anonymous public story submission

[maebeale]

Context

The Story Share portal (/story_shares) now has a signed-in "Share your story" page that reuses the existing StoryIdea flow (see the portal-parity PR). This mirrors the live WordPress site's /share/ form in spirit, but the WP form is fully anonymous — any visitor can submit without an account.

Our StoryIdea model can't be anonymous today: it requires a created_by User and an organization_id drawn from the submitter's own organizations.

What's needed for anonymous submission

• Add submitter identity columns to story_ideas (e.g. submitter_name, submitter_email, free-text submitter_organization) so a story can be attributed without a User/Organization record.
• Attribute anonymous submissions to a system/sentinel user (or make created_by optional with a guard).
• Relax StoryIdeaPolicy#new?/create? to allow guests for the portal route only (keep the admin index/show gated).
• Spam protection (reCAPTCHA/hCaptcha or honeypot + rate limiting) — the WP form is reCAPTCHA-gated.
• Consent checkbox matching the WP form's permission language.
• Moderation: anonymous submissions land in the existing admin review queue; titles are editorial (the WP form has no title field).

Parity notes (from stories.awbw.org research)

• WP /share/ fields: first/last name, name-display preference (full / first-only / hide), email (not published), organization (free text), state (free text), workshop name, featured image/video, YouTube URL, story body, additional images, category checkboxes (sectors), audience checkboxes, consent checkbox. No title.
• WP's anonymity is a real privacy bug (full name is in the HTML, hidden with CSS; email is exposed via the open REST API). Our version must handle credit server-side via AuthorCreditable and never render or expose hidden identity.

Out of scope

Signed-in submission already ships in the portal-parity work; this issue covers only the anonymous path.