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>

tests/dump.txt

@@ -1,8 +1,30 @@
 *** CGI VARIABLES ***
 *** GLOBAL VARIABLES ***
+=[xxx]
+addition=[8]
+complete=[ABCD;tohex]
+division=[1.666666666667]
+divisor=[8]
+error=[64]
+exprnumbers=[0123456789]
+include=[yes]
+ix=[1]
+lefty=[01234]
+modified1=[ABCD]
+multiplication=[15]
+nested=[64]
+newname=[another container value]
+noeval=[this is the value store in $[%name1].]
+numbers=[0123456789]
+subtraction=[2]
+theexpr=[bcd]
+thename=[this is the value store in .]
+tohex=[tohex]
+varname1=[vardata]
 *** LOCAL VARIABLES ***
+localvar=[This is a container set with '']
+testinclude=[xThis is a container set with ''x]
 *** KEYWORD VALUES ***
-cgi=[yes]
-sessiondir=[.]
+file=[./testinclude.jet]
+name1=[]
 *** COOKIES ***
-session=[18fd56a83f]