feat(discover): add user-defined extension→language mappings via config files

Read extra_extensions from ~/.config/codebase-memory-mcp/config.json
(global) and {repo}/.codebase-memory.json (project), merging them with
project config taking precedence. Unknown language values warn and skip.
Missing files are silently ignored (fail-open).

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

Author: shanemccarron-maker

Makefile.cbm

@@ -148,6 +148,7 @@ MCP_SRCS = src/mcp/mcp.c
 # Discover module (new)
 DISCOVER_SRCS = \
     src/discover/language.c \
+    src/discover/userconfig.c \
     src/discover/gitignore.c \
     src/discover/discover.c
 
@@ -259,6 +260,7 @@ TEST_MCP_SRCS = \
 
 TEST_DISCOVER_SRCS = \
     tests/test_language.c \
+    tests/test_userconfig.c \
     tests/test_gitignore.c \
     tests/test_discover.c
 

src/discover/language.c

@@ -3,8 +3,11 @@
  *
  * Maps file extensions and special filenames to CBMLanguage enum values.
  * Handles .m disambiguation (Objective-C vs Magma vs MATLAB).
+ * Consults the process-global user config (set via cbm_set_user_lang_config)
+ * before the built-in lookup table.
  */
 #include "discover/discover.h"
+#include "discover/userconfig.h"
 #include "cbm.h" // CBMLanguage, CBM_LANG_*
 
 #include <ctype.h>
@@ -354,6 +357,15 @@ CBMLanguage cbm_language_for_extension(const char *ext) {
         return CBM_LANG_COUNT;
     }
 
+    /* Check user-defined overrides first */
+    const cbm_userconfig_t *ucfg = cbm_get_user_lang_config();
+    if (ucfg) {
+        CBMLanguage ulang = cbm_userconfig_lookup(ucfg, ext);
+        if (ulang != CBM_LANG_COUNT) {
+            return ulang;
+        }
+    }
+
     for (size_t i = 0; i < EXT_TABLE_SIZE; i++) {
         if (strcmp(EXT_TABLE[i].ext, ext) == 0) {
             return EXT_TABLE[i].language;