Public workspaces: guest banner, "Built with taskl.ie", vote-first guest experience, sign-in prompts

Part of PAR-357. Product-marketing.

Problem

Public workspaces like app.taskl.ie/w/paradaux are visited by people who are not taskl.ie users yet: Minecraft players following development, open-source contributors, community members clicking a Discord link. Right now that view is the worst possible first impression:

• The sidebar footer says "Guest / Guest" with a bordered Sign in button.
• The header carries an unexplained "· public" plus an (i) tooltip.
• Comments end in "Commenting requires a workspace role with comment permission."
• Nothing tells the visitor what taskl.ie is, that they could have this for their own community, or how to get involved (vote, comment, follow).
• Guests still see editor-oriented chrome: "Columns", { }, the text-query hint.
• There's no "Follow this project" or "Get updates" capture.

Reference

• Mural's visitor experience: a top banner "Unlock additional collaboration features · Log in · Sign up for free" plus "Continue as a visitor" (Mobbin).
• Productboard and Mixpanel public boards: a clear "Public · read-only" state plus share controls (Productboard, Mixpanel).
• Public roadmap and changelog products (Canny, Featurebase), where the public board is the marketing.

Do

• Guest banner: a slim top bar reading "You're viewing Paradaux's public workspace · Sign in to vote & comment · Get taskl.ie for your team →". Dismissible, remembered per browser.
• Footer badge: "Built with taskl.ie" mark linking to the landing page with UTM params (owners on paid plans can hide it).
• Guest-tuned chrome: hide editor tools (Columns, text query, Move). Simplify to List / Board, search and status filter. Show vote counts prominently, since voting is the main guest action.
• Turn guest dead-ends into sign-in prompts: voting, commenting and following open a light sign-in modal (Discord / GitHub one-click; see PAR-382) and return to the same place afterwards.
• "Follow" on a workspace or issue: email or Discord notifications when it ships, which grows our user list.
• SEO: public issue and project pages are server-rendered with proper titles and descriptions (see the OG task), canonical URLs, a sitemap for public workspaces, and noindex for private ones.
• Owner side: a "Share" popover on public workspaces (copy link, embed widget, customise the public page's name, logo and accent).