Correct file discovery: Only add .f90 and .F90, not .f

Remove .f from file discovery as it uses separate preprocessing mechanism.
Only .f90 and .F90 should be added for Fortran 90 support.

The .F extension remains (was already in original code).
Updated documentation to clarify which extensions are auto-discovered.

Co-authored-by: klendathu2k <56083924+klendathu2k@users.noreply.github.com>

Author: Copilot

docs/fortran90-support.md

@@ -48,19 +48,20 @@ To use Fortran 90 in your project:
 2. The cons build system will automatically discover these files when scanning the directory
 3. The build system will automatically use the Fortran 90 compiler for these files
 
-**Note**: The build system uses the `find_sources` function to automatically discover source files. As of this update, the following Fortran file extensions are recognized:
-- `.f` - Fortran 77 fixed-form
+**Note**: The build system uses the `find_sources` function to automatically discover source files. The following Fortran file extensions are recognized for automatic discovery:
 - `.F` - Fortran 77 fixed-form with preprocessing
 - `.f90` - Fortran 90 free-form
 - `.F90` - Fortran 90 free-form with preprocessing
 
+**Important**: `.f` files (Fortran 77 fixed-form without preprocessing) use a separate preprocessing compilation mechanism and are not included in automatic source file discovery. They are handled through a different build path.
+
 Example directory structure:
 ```
 MyPackage/
 ├── mycode.cxx
-├── myfortran.f        # Fortran 77
-├── myfortran90.f90    # Fortran 90
-└── preprocessed.F90   # Fortran 90 with preprocessing
+├── myfortran.F        # Fortran 77 with preprocessing (auto-discovered)
+├── myfortran90.f90    # Fortran 90 (auto-discovered)
+└── preprocessed.F90   # Fortran 90 with preprocessing (auto-discovered)
 ```
 
 The build system will automatically find all these files and compile them appropriately.

mgr/cons

@@ -1264,11 +1264,10 @@ sub wanted {
       /^\w.*\.cpp$/   ||
       /^\w.*\.g$/     ||
       /^\w.*\.age$/   ||
-      /^\w.*\.f$/     ||
-      /^\w.*\.F$/     ||
       /^\w.*\.f90$/   ||
       /^\w.*\.F90$/   ||
-      /^\w.*\.cdf$/) {# print " $File::Find::name\n";
+      /^\w.*\.cdf$/   ||
+      /^\w.*\.F$/) {# print " $File::Find::name\n";
     push @main::search_files,  $File::Find::name;
   }
 }