Fix all memory leaks, vendor sqlite3, add Docker test infrastructure

Leak fixes (13 sources, 1.4MB → 0 bytes):
- Cypher: free col_names after rb_set_columns, free rejected inline
  prop nodes, store WITH aliases in qualified_name for auto-cleanup
- Store: add cbm_project_free_fields, fix find_node_ids_by_qns leak
- Graph buffer: free strdup'd hash keys during delete operations
- SQL scanner: free old start_tag before reassignment in deserialize

Platform independence:
- Vendor sqlite3 amalgamation (3.49.1) — eliminates system libsqlite3
  dependency, enables full ASan/LeakSanitizer instrumentation
- Add -I for vendored tree-sitter unicode headers — eliminates hidden
  dependency on system libicu-dev
- Add test-infrastructure/ with Docker Compose for local GCC+ASan
  testing that mirrors CI exactly

vendored/sqlite3/sqlite3ext.h

@@ -366,12 +366,6 @@ struct sqlite3_api_routines {
   /* Version 3.44.0 and later */
   void *(*get_clientdata)(sqlite3*,const char*);
   int (*set_clientdata)(sqlite3*, const char*, void*, void(*)(void*));
-  /* Version 3.50.0 and later */
-  int (*setlk_timeout)(sqlite3*,int,int);
-  /* Version 3.51.0 and later */
-  int (*set_errmsg)(sqlite3*,int,const char*);
-  int (*db_status64)(sqlite3*,int,sqlite3_int64*,sqlite3_int64*,int);
-  
 };
 
 /*
@@ -705,11 +699,6 @@ typedef int (*sqlite3_loadext_entry)(
 /* Version 3.44.0 and later */
 #define sqlite3_get_clientdata         sqlite3_api->get_clientdata
 #define sqlite3_set_clientdata         sqlite3_api->set_clientdata
-/* Version 3.50.0 and later */
-#define sqlite3_setlk_timeout          sqlite3_api->setlk_timeout
-/* Version 3.51.0 and later */
-#define sqlite3_set_errmsg             sqlite3_api->set_errmsg
-#define sqlite3_db_status64            sqlite3_api->db_status64
 #endif /* !defined(SQLITE_CORE) && !defined(SQLITE_OMIT_LOAD_EXTENSION) */
 
 #if !defined(SQLITE_CORE) && !defined(SQLITE_OMIT_LOAD_EXTENSION)