Fix dead civicsuite.github.io links (org transfer)

[scottconverse]

Summary

• civicsuite.github.io (the old CivicSuite org's GitHub Pages site) returns 404 as of the 2026-08-12 org transfer to townlight -- GitHub's repo/org-transfer redirect covers github.com repo URLs and the API, but not Pages hostnames.
• Three "explore the product" links in this repo pointed at that dead host: README.md:13, profile/README.md:12, profile/README.md:43, and site/index.html:52.
• Repointed all four to https://townlight.github.io/townlight/, the live successor product-docs Pages site (verified 200, serving the real product landing page). This is distinct from https://townlight.github.io/.github/, which is this repo's own org front-door and would be self-referential if used here.

Out of scope (left as-is)

• github.com/CivicSuite/... links elsewhere in these same files still resolve fine (200) via GitHub's transfer redirect, so they were not touched -- that's a separate, lower-urgency cleanup across the org, not an active break.

Test plan

• Verified https://civicsuite.github.io/civicsuite/ returns 404 (repro)
• Verified https://townlight.github.io/townlight/ returns 200 with real product content
• Confirmed tests/test_public_site.py does not assert on the literal old URL, so the contract test suite is unaffected
• CI (Pages deploy workflow's test job / python -m unittest discover -s tests) will run on this PR

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