Clean up TODO.txt/testjet.jet, gitignore jetc build byproducts

TODO.txt: drop the stale "Fix the variable retriever..." bug-list entry -
long since fixed. tests/testjet.jet: cgi="true" -> cgi="yes", matching the
deliberate "yes" convention already used elsewhere (__jet.cpp checks
resolveKeyword("cgi") == "yes", not "true"). tests/dump.txt: regenerated
output from re-running the test after the above.

.gitignore: jetc/ was accumulating untracked build output (compiled .cpp,
binaries, .pic.o, .so, libCoreUtils_pic.a) alongside its real tracked
source - ignore the generated artifacts, keep the two worked-example
.jet templates explicitly un-ignored since *.cpp/no-extension patterns
would otherwise also catch demo.jet/demo2.jet's own extension-less
compiled binaries without excluding the .jet sources themselves.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

TODO.txt

@@ -9,7 +9,4 @@ file name and content length from variable. $[data(filename)] and
 $[data(length)] possibly.
 4) 
 
-BUG LIST
 
-1) Fix the variable retriever to perform all variable translation
-before fetching value processing.