feat(footer): use @profullstack/footer

[ralyodio]

Renders the copyright line and the Profullstack ring nav (<< Profullstack >>, random, vote) with @profullstack/footer (latest), server-side, so template updates published to the package reach this site without a redeploy. The hand-written ring nav is removed so the ring appears once.

The landing page is a static file that setup.sh writes and Caddy's file_server serves, so this uses the package's static pattern. The CLI-rendered footer is pasted into the heredoc with ${DOMAIN} in the from= links, inside <footer data-profullstack-footer>; that is what the ring verifier reads. embed.js from jsDelivr swaps in the @latest template in the browser, and Caddy sends no CSP, so nothing else changes. The AgentBBS one-liner footer text is kept, and the old ring nav and its .webring CSS are removed. Checks: bash -n is clean, shellcheck has no new warnings, and the rendered heredoc has the three ring links with from=https://bbs.profullstack.com/ (screenshot-checked).

🤖 Generated with Claude Code

[github-actions]

ThreatCrush Security Scan

10 finding(s)

HIGH/CRITICAL: 7 | LOW: 3

Severity	Rule	Location
HIGH	secret-generic-credential	deploy/ergo/ircd.yaml:162
HIGH	secret-generic-credential	deploy/ergo/ircd.yaml:221
HIGH	secret-generic-credential	deploy/ergo/ircd.yaml:638
HIGH	secret-generic-credential	deploy/ergo/ircd.yaml:787
HIGH	secret-database-url	deploy/ergo/ircd.yaml:893
HIGH	secret-generic-credential	deploy/ergo/ircd.yaml:1025
HIGH	secret-generic-credential	deploy/ergo/ircd.yaml:1033
LOW	secret-generic-credential	deploy/ergo/ircd.yaml:772
LOW	tls-verification-disabled	internal/mail/mail.go:109
LOW	secret-generic-credential	internal/mailu/mailu_test.go:44

Snippets are redacted; ThreatCrush never prints matched credential material.