chore: Significantly restructure folder layout

This moves the various projects from "type-based" folders (such as
"services" or "tools") into more appropriate semantic folders (such as
"nix", "ops" or "web").

Deprecated projects (nixcon-demo & gotest) which only existed for
testing/demonstration purposes have been removed.

(Note: *all* builds are broken with this commit)

web/cgit-taz/default.nix

@@ -0,0 +1,69 @@
+# This derivation configures a 'cgit' instance to serve repositories
+# from a different source.
+#
+# In the first round this will just serve my GitHub repositories until
+# I'm happy with the display.
+
+{ pkgs, ... }:
+
+with pkgs.third_party;
+
+let
+  # Patched version of cgit that builds repository URLs correctly
+  # (since only one repository is served)
+  monocgit = cgit.overrideAttrs(old: {
+    patches = old.patches ++ [ ./cgit_depot_url.patch ];
+  });
+
+  cgitConfig = writeText "cgitrc" ''
+    # Global configuration
+    virtual-root=/
+    enable-http-clone=1
+    readme=:README.md
+    about-filter=${monocgit}/lib/cgit/filters/about-formatting.sh
+    source-filter=${monocgit}/lib//cgit/filters/syntax-highlighting.py
+
+    # Repository configuration
+    repo.url=depot
+    repo.path=/git/depot/.git
+    repo.desc=tazjin's personal monorepo
+    repo.owner=tazjin <mail@tazj.in>
+    repo.clone-url=https://git.tazj.in ssh://source.developers.google.com:2022/p/tazjins-infrastructure/r/depot
+    repo.enable-remote-branches=1
+  '';
+
+  thttpdConfig = writeText "thttpd.conf" ''
+    port=8080
+    dir=${monocgit}/cgit
+    nochroot
+    novhost
+    logfile=/dev/stdout
+    cgipat=**.cgi
+  '';
+
+  # Patched version of thttpd that serves cgit.cgi as the index and
+  # sets the environment variable for pointing cgit at the correct
+  # configuration.
+  #
+  # Things are done this way because recompilation of thttpd is much
+  # faster than cgit and I don't want to wait long when iterating on
+  # config.
+  thttpdConfigPatch = writeText "thttpd_cgit_conf.patch" ''
+    diff --git a/libhttpd.c b/libhttpd.c
+    index c6b1622..eef4b73 100644
+    --- a/libhttpd.c
+    +++ b/libhttpd.c
+    @@ -3055,4 +3055,6 @@ make_envp( httpd_conn* hc )
+
+         envn = 0;
+    +    // force cgit to load the correct configuration
+    +    envp[envn++] = "CGIT_CONFIG=${cgitConfig}";
+         envp[envn++] = build_env( "PATH=%s", CGI_PATH );
+     #ifdef CGI_LD_LIBRARY_PATH
+  '';
+  thttpdCgit = thttpd.overrideAttrs(old: {
+    patches = [ ./cgit_idx.patch thttpdConfigPatch ];
+  });
+in writeShellScriptBin "cgit-launch" ''
+  exec ${thttpdCgit}/bin/thttpd -D -C ${thttpdConfig}
+# ''