tcl: proc + uplevel + upvar + global + variable + info (+19 tests, 225 total)

Phase 3 headline feature: everything falls out of SX's first-class env chain.
- make-tcl-interp extended with :frame-stack and :procs fields
- proc: user-defined commands with param binding, rest args, isolated scope
- uplevel: run script in ancestor frame with correct frame propagation
- upvar: alias local name to remote frame variable (get/set follow alias)
- global/variable: sugar for upvar #0
- info: level, vars, locals, globals, commands, procs, args, body
- tcl-call-proc propagates updated frames back to caller after proc returns
- test.sh timeout bumped to 90s for larger runtime

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/tcl/test.sh

@@ -40,7 +40,7 @@ cat > "$TMPFILE" << EPOCHS
 (eval "tcl-test-summary")
 EPOCHS
 
-OUTPUT=$(timeout 30 "$SX_SERVER" < "$TMPFILE" 2>&1)
+OUTPUT=$(timeout 90 "$SX_SERVER" < "$TMPFILE" 2>&1)
 [ "$VERBOSE" = "-v" ] && echo "$OUTPUT"
 
 # Extract summary line from epoch 7 output