Add project task visibility controls and public read views #211

Work

Add a compact Private / Organization / Public selector to project task creation and authorized editing. Explain who can read the task. Show organization/public options only when valid for that project, with useful reasons when unavailable. Existing tasks remain in project navigation and read/edit views.

Acceptance

• Visibility shown clearly without adding redundant headings or oversized pills.
• Explicit changes preserve unsaved text and current-version checks.
• Public project visitors can read public tasks only; editing and claiming require authorization.
• Private titles, child counts, assignment contact data and related items stay hidden.
• Parent-child visibility conflicts have an actionable response.
• Mobile, keyboard, back navigation and live permission changes verified.

Dependencies

#207 and #209; reuse existing task forms and read views. No standalone personal/organization task pages.