fix(governance): upgrade two HTTP links to HTTPS in playground

`governance / Well-Known (RFC 9116 + RSR)` step rejects mixed-content
(HTTP links in HTML). Two external links in echidna-playground/index.html
still used http:// — both targets serve HTTPS.

  http://ssr.msr-inria.inria.fr/  → https://...
  http://www.mines-paristech.eu   → https://...

Last governance failure on main; remaining failures (K9, A2ML, Julia,
MSRV, MVP Smoke, PR address) are content-level, out of scope for the
baseline-rot sweep.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

echidna-playground/index.html

@@ -71,7 +71,7 @@ <h4>A First Example: The Infinitude of Primes</h4>
               We don't provide a Coq tutorial (yet), but as a showcase, we
               display a proof of the infinitude of primes in Coq. The proof relies
               in the Mathematical Components library by the
-              <a href="http://ssr.msr-inria.inria.fr/">MSR/Inria</a> team led
+              <a href="https://ssr.msr-inria.inria.fr/">MSR/Inria</a> team led
               by Georges Gonthier, so our first step will be to load it and
               set a few Coq options:
             </p>
@@ -169,7 +169,7 @@ <h5>Ready to do Proofs!</h5>
               <li>
                 Benoît Pin
                 (<a href="https://www.cri.ensmp.fr/">CRI</a>,
-                <a href="http://www.mines-paristech.eu">MINES ParisTech</a>)
+                <a href="https://www.mines-paristech.eu">MINES ParisTech</a>)
               </li>
             </ul>
           </div>