chore: rewrite uses of cs.tvl.fyi to code.tvl.fyi

I've checked the new links manually.

- //web/tvl: changed the target path of links to the tvix docs since
  they were moved in r/2378.

- //users/aspen/resume: Tvix is no longer //third_party/nix.

Change-Id: I419bae1a46bdccc7baa7327215aa2368ffc0f01c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/13043
Reviewed-by: aspen <root@gws.fyi>
Tested-by: BuildkiteCI
Autosubmit: sterni <sternenseemann@systemli.org>
Reviewed-by: fogti <fogti+devel@ytrizja.de>
Reviewed-by: tazjin <tazjin@tvl.su>

users/tazjin/blog/default.nix

@@ -14,7 +14,7 @@ let
       <p class="footer">
         <a class="uncoloured-link" href="https://tazj.in">homepage</a>
         |
-        <a class="uncoloured-link" href="https://cs.tvl.fyi/">code</a>
+        <a class="uncoloured-link" href="https://code.tvl.fyi/">code</a>
       </p>
       <p class="lod">ಠ_ಠ</p>
     '';